diff --git a/app/Http/Controllers/Landlord/TenantController.php b/app/Http/Controllers/Landlord/TenantController.php
index 6137b77..d33069f 100644
--- a/app/Http/Controllers/Landlord/TenantController.php
+++ b/app/Http/Controllers/Landlord/TenantController.php
@@ -84,6 +84,24 @@ class TenantController extends Controller
     {
         $tenant = Tenant::with('domains')->findOrFail($id);
 
+        $tokens = [];
+        try {
+            tenancy()->initialize($tenant);
+            $user = \App\Modules\Core\Models\User::first();
+            if ($user) {
+                $tokens = $user->tokens()->orderBy('created_at', 'desc')->get(['id', 'name', 'last_used_at', 'created_at'])->map(function($token) {
+                    return [
+                        'id' => $token->id,
+                        'name' => $token->name,
+                        'last_used_at' => $token->last_used_at ? $token->last_used_at->format('Y-m-d H:i') : '未使用',
+                        'created_at' => $token->created_at->format('Y-m-d H:i'),
+                    ];
+                });
+            }
+        } catch (\Exception $e) {
+            \Log::warning("Failed to fetch tokens for tenant {$id}: " . $e->getMessage());
+        }
+
         return Inertia::render('Landlord/Tenant/Show', [
             'tenant' => [
                 'id' => $tenant->id,
@@ -98,6 +116,7 @@ class TenantController extends Controller
                     'domain' => $d->domain,
                 ])->toArray(),
             ],
+            'tokens' => $tokens,
         ]);
     }
 
@@ -242,4 +261,58 @@ class TenantController extends Controller
 
         return redirect()->back()->with('success', '樣式設定已更新');
     }
+
+    /**
+     * 建立 API Token (用於 POS)
+     */
+    public function createToken(Request $request, Tenant $tenant)
+    {
+        $request->validate([
+            'name' => 'required|string|max:50',
+        ]);
+
+        try {
+            // 切換至租戶環境
+            tenancy()->initialize($tenant);
+
+            // 尋找超級管理員 (假設 ID 1, 或者根據 Role)
+            // 這裡簡單取第一個使用者，通常是 Admin
+            $user = \App\Modules\Core\Models\User::first();
+
+            if (!$user) {
+                return back()->with('error', '該租戶尚無使用者，無法建立 Token。');
+            }
+
+            // 建立 Token
+            $token = $user->createToken($request->name);
+
+            return back()->with('success', 'Token 建立成功')->with('new_token', $token->plainTextToken);
+        } catch (\Exception $e) {
+            \Log::error("Token creation failed: " . $e->getMessage());
+            return back()->with('error', 'Token 建立失敗');
+        } finally {
+             // tenancy()->end(); // Laravel Tenancy 自動處理 scope 結束? 通常 Controller request life-cycle?
+             // Landlord controller is Central. Tenancy initialization persists for request.
+             // We should explicit end if we want to be safe, but redirect ends request anyway.
+        }
+    }
+
+    /**
+     * 撤銷 API Token
+     */
+    public function revokeToken(Request $request, Tenant $tenant, string $tokenId)
+    {
+        try {
+            tenancy()->initialize($tenant);
+            $user = \App\Modules\Core\Models\User::first();
+            
+            if ($user) {
+                $user->tokens()->where('id', $tokenId)->delete();
+            }
+
+            return back()->with('success', 'Token 已撤銷');
+        } catch (\Exception $e) {
+            return back()->with('error', 'Token 撤銷失敗');
+        }
+    }
 }
diff --git a/app/Http/Middleware/HandleInertiaRequests.php b/app/Http/Middleware/HandleInertiaRequests.php
index ca4217e..679266f 100644
--- a/app/Http/Middleware/HandleInertiaRequests.php
+++ b/app/Http/Middleware/HandleInertiaRequests.php
@@ -61,6 +61,7 @@ class HandleInertiaRequests extends Middleware
             'flash' => [
                 'success' => $request->session()->get('success'),
                 'error' => $request->session()->get('error'),
+                'new_token' => $request->session()->get('new_token'),
             ],
             'branding' => function () {
                 $tenant = tenancy()->tenant;
diff --git a/app/Modules/Core/Models/User.php b/app/Modules/Core/Models/User.php
index 7ac0e11..f91aec7 100644
--- a/app/Modules/Core/Models/User.php
+++ b/app/Modules/Core/Models/User.php
@@ -10,10 +10,12 @@ use Spatie\Permission\Traits\HasRoles;
 use Spatie\Activitylog\Traits\LogsActivity;
 use Spatie\Activitylog\LogOptions;
 
+use Laravel\Sanctum\HasApiTokens;
+
 class User extends Authenticatable
 {
     /** @use HasFactory<\Database\Factories\UserFactory> */
-    use HasFactory, Notifiable, HasRoles, LogsActivity;
+    use HasFactory, Notifiable, HasRoles, LogsActivity, HasApiTokens;
 
     /**
      * 可批量賦值的屬性。
diff --git a/app/Modules/Integration/Controllers/OrderSyncController.php b/app/Modules/Integration/Controllers/OrderSyncController.php
new file mode 100644
index 0000000..dfa4f89
--- /dev/null
+++ b/app/Modules/Integration/Controllers/OrderSyncController.php
@@ -0,0 +1,109 @@
+<?php
+
+namespace App\Modules\Integration\Controllers;
+
+use App\Http\Controllers\Controller;
+use Illuminate\Http\Request;
+use App\Modules\Integration\Models\SalesOrder;
+use App\Modules\Integration\Models\SalesOrderItem;
+use App\Modules\Inventory\Services\InventoryService;
+use App\Modules\Inventory\Models\Product;
+use App\Modules\Inventory\Models\Warehouse;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Log;
+
+class OrderSyncController extends Controller
+{
+    protected $inventoryService;
+
+    public function __construct(InventoryService $inventoryService)
+    {
+        $this->inventoryService = $inventoryService;
+    }
+
+    public function store(Request $request)
+    {
+        $request->validate([
+            'external_order_id' => 'required|string|unique:sales_orders,external_order_id',
+            'warehouse' => 'nullable|string',
+            'warehouse_id' => 'nullable|exists:warehouses,id',
+            'items' => 'required|array',
+            'items.*.pos_product_id' => 'required|string',
+            'items.*.qty' => 'required|numeric|min:0.0001',
+            'items.*.price' => 'required|numeric',
+        ]);
+
+        try {
+            return DB::transaction(function () use ($request) {
+                // 1. Create Order
+                $order = SalesOrder::create([
+                    'external_order_id' => $request->external_order_id,
+                    'status' => 'completed',
+                    'payment_method' => $request->payment_method ?? 'cash',
+                    'total_amount' => 0, // Will calculate
+                    'sold_at' => $request->sold_at ?? now(),
+                    'raw_payload' => $request->all(),
+                ]);
+
+                // Find Warehouse (Default to "銷售倉庫")
+                $warehouseId = $request->warehouse_id;
+                
+                if (empty($warehouseId)) {
+                    $warehouseName = $request->warehouse ?: '銷售倉庫';
+                    $warehouse = Warehouse::firstOrCreate(['name' => $warehouseName], [
+                        'code' => 'SALES-' . strtoupper(bin2hex(random_bytes(4))),
+                        'type' => 'system_sales',
+                        'is_active' => true,
+                    ]);
+                    $warehouseId = $warehouse->id;
+                }
+
+                $totalAmount = 0;
+
+                foreach ($request->items as $itemData) {
+                    // Find product by external ID (Strict Check)
+                    $product = Product::where('external_pos_id', $itemData['pos_product_id'])->first();
+
+                    if (!$product) {
+                        throw new \Exception("Product not found for POS ID: " . $itemData['pos_product_id'] . ". Please sync product first.");
+                    }
+
+                    $qty = $itemData['qty'];
+                    $price = $itemData['price'];
+                    $lineTotal = $qty * $price;
+                    $totalAmount += $lineTotal;
+
+                    // 2. Create Order Item
+                    SalesOrderItem::create([
+                        'sales_order_id' => $order->id,
+                        'product_id' => $product->id,
+                        'product_name' => $product->name, // Snapshot name
+                        'quantity' => $qty,
+                        'price' => $price,
+                        'total' => $lineTotal,
+                    ]);
+
+                    // 3. Deduct Stock (Force negative allowed for POS orders)
+                    $this->inventoryService->decreaseStock(
+                        $product->id,
+                        $warehouseId,
+                        $qty,
+                        "POS Order: " . $order->external_order_id,
+                        true // Force = true
+                    );
+                }
+
+                $order->update(['total_amount' => $totalAmount]);
+
+                return response()->json([
+                    'message' => 'Order synced and stock deducted successfully',
+                    'order_id' => $order->id,
+                ], 201);
+            });
+
+        } catch (\Exception $e) {
+            Log::error('Order Sync Failed', ['error' => $e->getMessage(), 'payload' => $request->all()]);
+            return response()->json(['message' => 'Sync failed: ' . $e->getMessage()], 400);
+        }
+    }
+}
diff --git a/app/Modules/Integration/Controllers/ProductSyncController.php b/app/Modules/Integration/Controllers/ProductSyncController.php
new file mode 100644
index 0000000..af939ff
--- /dev/null
+++ b/app/Modules/Integration/Controllers/ProductSyncController.php
@@ -0,0 +1,47 @@
+<?php
+
+namespace App\Modules\Integration\Controllers;
+
+use App\Http\Controllers\Controller;
+use Illuminate\Http\Request;
+use App\Modules\Inventory\Services\ProductService;
+use Illuminate\Support\Facades\Log;
+
+class ProductSyncController extends Controller
+{
+    protected $productService;
+
+    public function __construct(ProductService $productService)
+    {
+        $this->productService = $productService;
+    }
+
+    public function upsert(Request $request)
+    {
+        $request->validate([
+            'external_pos_id' => 'required|string',
+            'name' => 'required|string',
+            'price' => 'nullable|numeric',
+            'sku' => 'nullable|string',
+            'barcode' => 'nullable|string',
+            'category' => 'nullable|string',
+            'unit' => 'nullable|string',
+            'updated_at' => 'nullable|date',
+        ]);
+
+        try {
+            $product = $this->productService->upsertFromPos($request->all());
+
+            return response()->json([
+                'message' => 'Product synced successfully',
+                'data' => [
+                    'id' => $product->id,
+                    'external_pos_id' => $product->external_pos_id,
+                ]
+            ]);
+        } catch (\Exception $e) {
+            Log::error('Product Sync Failed', ['error' => $e->getMessage(), 'payload' => $request->all()]);
+            return response()->json(['message' => 'Sync failed'], 500);
+        }
+    }
+}
diff --git a/app/Modules/Integration/IntegrationServiceProvider.php b/app/Modules/Integration/IntegrationServiceProvider.php
new file mode 100644
index 0000000..1ea7da9
--- /dev/null
+++ b/app/Modules/Integration/IntegrationServiceProvider.php
@@ -0,0 +1,24 @@
+<?php
+
+namespace App\Modules\Integration;
+
+use Illuminate\Support\ServiceProvider;
+use Illuminate\Support\Facades\Route;
+use App\Modules\Integration\Middleware\TenantIdentificationMiddleware;
+
+class IntegrationServiceProvider extends ServiceProvider
+{
+    public function boot()
+    {
+        $this->loadRoutesFrom(__DIR__ . '/Routes/api.php');
+        $this->loadMigrationsFrom(__DIR__ . '/Database/Migrations');
+
+        // Register Middleware Alias
+        Route::aliasMiddleware('integration.tenant', TenantIdentificationMiddleware::class);
+    }
+
+    public function register()
+    {
+        //
+    }
+}
diff --git a/app/Modules/Integration/Middleware/TenantIdentificationMiddleware.php b/app/Modules/Integration/Middleware/TenantIdentificationMiddleware.php
new file mode 100644
index 0000000..eb705f6
--- /dev/null
+++ b/app/Modules/Integration/Middleware/TenantIdentificationMiddleware.php
@@ -0,0 +1,58 @@
+<?php
+
+namespace App\Modules\Integration\Middleware;
+
+use Closure;
+use Illuminate\Http\Request;
+use Stancl\Tenancy\Facades\Tenancy;
+use Symfony\Component\HttpFoundation\Response;
+
+class TenantIdentificationMiddleware
+{
+    /**
+     * Handle an incoming request.
+     *
+     * @param  \Closure(\Illuminate\Http\Request): (\Symfony\Component\HttpFoundation\Response)  $next
+     */
+    public function handle(Request $request, Closure $next): Response
+    {
+        // 1. Check for X-Tenant-Domain header
+        $domain = $request->header('X-Tenant-Domain');
+
+        if (! $domain) {
+            return response()->json([
+                'message' => 'Missing X-Tenant-Domain header.',
+            ], 400);
+        }
+
+        // 2. Find Tenant by domain
+        // Assuming domains are stored in 'domains' table and linked to tenants
+        // Or using Stancl's tenant finder. 
+        // Stancl Tenancy usually finds by domain automatically for web routes, but for API 
+        // we are doing manual identification because we might not be using subdomains for API calls (or maybe we are).
+        // If the API endpoint is centrally hosted (e.g. api.star-erp.com/v1/...), we need this header.
+        
+        // Let's try to initialize tenancy manually.
+        // We need to find the tenant model that has this domain.
+        try {
+             $tenant = \App\Modules\Core\Models\Tenant::whereHas('domains', function ($query) use ($domain) {
+                 $query->where('domain', $domain);
+             })->first();
+
+             if (! $tenant) {
+                 return response()->json([
+                     'message' => 'Tenant not found.',
+                 ], 404);
+             }
+
+             Tenancy::initialize($tenant);
+
+        } catch (\Exception $e) {
+            return response()->json([
+                'message' => 'Tenant initialization failed: ' . $e->getMessage(),
+            ], 500);
+        }
+
+        return $next($request);
+    }
+}
diff --git a/app/Modules/Integration/Models/SalesOrder.php b/app/Modules/Integration/Models/SalesOrder.php
new file mode 100644
index 0000000..450e560
--- /dev/null
+++ b/app/Modules/Integration/Models/SalesOrder.php
@@ -0,0 +1,31 @@
+<?php
+
+namespace App\Modules\Integration\Models;
+
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\HasMany;
+
+class SalesOrder extends Model
+{
+    protected $table = 'sales_orders';
+
+    protected $fillable = [
+        'external_order_id',
+        'status',
+        'payment_method',
+        'total_amount',
+        'sold_at',
+        'raw_payload',
+    ];
+
+    protected $casts = [
+        'sold_at' => 'datetime',
+        'raw_payload' => 'array',
+        'total_amount' => 'decimal:4',
+    ];
+
+    public function items(): HasMany
+    {
+        return $this->hasMany(SalesOrderItem::class);
+    }
+}
diff --git a/app/Modules/Integration/Models/SalesOrderItem.php b/app/Modules/Integration/Models/SalesOrderItem.php
new file mode 100644
index 0000000..dd7c048
--- /dev/null
+++ b/app/Modules/Integration/Models/SalesOrderItem.php
@@ -0,0 +1,31 @@
+<?php
+
+namespace App\Modules\Integration\Models;
+
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
+
+class SalesOrderItem extends Model
+{
+    protected $table = 'sales_order_items';
+
+    protected $fillable = [
+        'sales_order_id',
+        'product_id',
+        'product_name',
+        'quantity',
+        'price',
+        'total',
+    ];
+
+    protected $casts = [
+        'quantity' => 'decimal:4',
+        'price' => 'decimal:4',
+        'total' => 'decimal:4',
+    ];
+
+    public function order(): BelongsTo
+    {
+        return $this->belongsTo(SalesOrder::class, 'sales_order_id');
+    }
+}
diff --git a/app/Modules/Integration/Routes/api.php b/app/Modules/Integration/Routes/api.php
new file mode 100644
index 0000000..571c93c
--- /dev/null
+++ b/app/Modules/Integration/Routes/api.php
@@ -0,0 +1,12 @@
+<?php
+
+use Illuminate\Support\Facades\Route;
+use App\Modules\Integration\Controllers\ProductSyncController;
+use App\Modules\Integration\Controllers\OrderSyncController;
+
+Route::prefix('api/v1/integration')
+    ->middleware(['api', 'integration.tenant', 'auth:sanctum']) // integration.tenant middleware to identify tenant
+    ->group(function () {
+        Route::post('products/upsert', [ProductSyncController::class, 'upsert']);
+        Route::post('orders', [OrderSyncController::class, 'store']);
+    });
diff --git a/app/Modules/Inventory/Contracts/InventoryServiceInterface.php b/app/Modules/Inventory/Contracts/InventoryServiceInterface.php
index f77cd98..2bf631a 100644
--- a/app/Modules/Inventory/Contracts/InventoryServiceInterface.php
+++ b/app/Modules/Inventory/Contracts/InventoryServiceInterface.php
@@ -21,9 +21,10 @@ interface InventoryServiceInterface
      * @param int $warehouseId
      * @param float $quantity
      * @param string|null $reason
+     * @param bool $force
      * @return void
      */
-    public function decreaseStock(int $productId, int $warehouseId, float $quantity, ?string $reason = null): void;
+    public function decreaseStock(int $productId, int $warehouseId, float $quantity, ?string $reason = null, bool $force = false): void;
 
     /**
      * Get all active warehouses.
diff --git a/app/Modules/Inventory/Models/Product.php b/app/Modules/Inventory/Models/Product.php
index e243aba..771eba5 100644
--- a/app/Modules/Inventory/Models/Product.php
+++ b/app/Modules/Inventory/Models/Product.php
@@ -18,7 +18,9 @@ class Product extends Model
     protected $fillable = [
         'code',
         'barcode',
+        'sku',
         'name',
+        'external_pos_id',
         'category_id',
         'brand',
         'specification',
diff --git a/app/Modules/Inventory/Services/InventoryService.php b/app/Modules/Inventory/Services/InventoryService.php
index 314371d..ece5d17 100644
--- a/app/Modules/Inventory/Services/InventoryService.php
+++ b/app/Modules/Inventory/Services/InventoryService.php
@@ -59,9 +59,9 @@ class InventoryService implements InventoryServiceInterface
         return $stock >= $quantity;
     }
 
-    public function decreaseStock(int $productId, int $warehouseId, float $quantity, ?string $reason = null): void
+    public function decreaseStock(int $productId, int $warehouseId, float $quantity, ?string $reason = null, bool $force = false): void
     {
-        DB::transaction(function () use ($productId, $warehouseId, $quantity, $reason) {
+        DB::transaction(function () use ($productId, $warehouseId, $quantity, $reason, $force) {
             $inventories = Inventory::where('product_id', $productId)
                 ->where('warehouse_id', $warehouseId)
                 ->where('quantity', '>', 0)
@@ -79,8 +79,30 @@ class InventoryService implements InventoryServiceInterface
             }
 
             if ($remainingToDecrease > 0) {
-                // 這裡可以選擇報錯或允許負庫存，目前為了嚴謹拋出異常
-                throw new \Exception("庫存不足，無法扣除所有請求的數量。");
+                if ($force) {
+                    // Find any existing inventory record in this warehouse to subtract from, or create one
+                    $inventory = Inventory::where('product_id', $productId)
+                        ->where('warehouse_id', $warehouseId)
+                        ->first();
+                    
+                    if (!$inventory) {
+                        $inventory = Inventory::create([
+                            'warehouse_id' => $warehouseId,
+                            'product_id' => $productId,
+                            'quantity' => 0,
+                            'unit_cost' => 0,
+                            'total_value' => 0,
+                            'batch_number' => 'POS-AUTO-' . time(),
+                            'arrival_date' => now(),
+                            'origin_country' => 'TW',
+                            'quality_status' => 'normal',
+                        ]);
+                    }
+                    
+                    $this->decreaseInventoryQuantity($inventory->id, $remainingToDecrease, $reason);
+                } else {
+                    throw new \Exception("庫存不足，無法扣除所有請求的數量。");
+                }
             }
         });
     }
diff --git a/app/Modules/Inventory/Services/ProductService.php b/app/Modules/Inventory/Services/ProductService.php
new file mode 100644
index 0000000..26b4bac
--- /dev/null
+++ b/app/Modules/Inventory/Services/ProductService.php
@@ -0,0 +1,73 @@
+<?php
+
+namespace App\Modules\Inventory\Services;
+
+use App\Modules\Inventory\Models\Product;
+use App\Modules\Inventory\Models\Category;
+use App\Modules\Inventory\Models\Unit;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Log;
+
+class ProductService
+{
+    /**
+     * Upsert product from external POS source.
+     *
+     * @param array $data
+     * @return Product
+     */
+    public function upsertFromPos(array $data)
+    {
+        return DB::transaction(function () use ($data) {
+            $externalId = $data['external_pos_id'] ?? null;
+
+            if (!$externalId) {
+                throw new \Exception("External POS ID is required for syncing.");
+            }
+
+            // Try to find by external_pos_id
+            $product = Product::where('external_pos_id', $externalId)->first();
+
+            if (!$product) {
+                // If not found, create new
+                // Optional: Check SKU conflict if needed, but for now trust POS ID
+                $product = new Product();
+                $product->external_pos_id = $externalId;
+            }
+
+            // Map allowed fields
+            $product->name = $data['name'];
+            $product->barcode = $data['barcode'] ?? $product->barcode;
+            $product->sku = $data['sku'] ?? $product->sku; // Maybe allow SKU update?
+            $product->price = $data['price'] ?? 0;
+            
+            // Generate Code if missing (use sku or external_id)
+            if (empty($product->code)) {
+                $product->code = $data['code'] ?? ($product->sku ?? $product->external_pos_id);
+            }
+            
+            // Handle Category (Default: 未分類)
+            if (empty($product->category_id)) {
+                $categoryName = $data['category'] ?? '未分類';
+                $category = Category::firstOrCreate(
+                    ['name' => $categoryName],
+                    ['code' => 'CAT-' . strtoupper(bin2hex(random_bytes(4)))]
+                );
+                $product->category_id = $category->id;
+            }
+
+            // Handle Base Unit (Default: 個)
+            if (empty($product->base_unit_id)) {
+                $unitName = $data['unit'] ?? '個';
+                $unit = Unit::firstOrCreate(['name' => $unitName]);
+                $product->base_unit_id = $unit->id;
+            }
+            
+            $product->is_active = $data['is_active'] ?? true;
+            
+            $product->save();
+
+            return $product;
+        });
+    }
+}
diff --git a/composer.json b/composer.json
index c95b4cb..65025cd 100644
--- a/composer.json
+++ b/composer.json
@@ -12,6 +12,7 @@
         "php": "^8.2",
         "inertiajs/inertia-laravel": "^2.0",
         "laravel/framework": "^12.0",
+        "laravel/sanctum": "^4.3",
         "laravel/tinker": "^2.10.1",
         "maatwebsite/excel": "^3.1",
         "spatie/laravel-activitylog": "^4.10",
diff --git a/composer.lock b/composer.lock
index aa484d6..a19c483 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "b3cbace7e72a7a68b5aefdd82bea205a",
+    "content-hash": "0efc099e328144f00fc558c52ff945c4",
     "packages": [
         {
             "name": "brick/math",
@@ -1673,6 +1673,69 @@
             },
             "time": "2025-11-21T20:52:52+00:00"
         },
+        {
+            "name": "laravel/sanctum",
+            "version": "v4.3.0",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/laravel/sanctum.git",
+                "reference": "c978c82b2b8ab685468a7ca35224497d541b775a"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/laravel/sanctum/zipball/c978c82b2b8ab685468a7ca35224497d541b775a",
+                "reference": "c978c82b2b8ab685468a7ca35224497d541b775a",
+                "shasum": ""
+            },
+            "require": {
+                "ext-json": "*",
+                "illuminate/console": "^11.0|^12.0",
+                "illuminate/contracts": "^11.0|^12.0",
+                "illuminate/database": "^11.0|^12.0",
+                "illuminate/support": "^11.0|^12.0",
+                "php": "^8.2",
+                "symfony/console": "^7.0"
+            },
+            "require-dev": {
+                "mockery/mockery": "^1.6",
+                "orchestra/testbench": "^9.15|^10.8",
+                "phpstan/phpstan": "^1.10"
+            },
+            "type": "library",
+            "extra": {
+                "laravel": {
+                    "providers": [
+                        "Laravel\\Sanctum\\SanctumServiceProvider"
+                    ]
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Laravel\\Sanctum\\": "src/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Taylor Otwell",
+                    "email": "taylor@laravel.com"
+                }
+            ],
+            "description": "Laravel Sanctum provides a featherweight authentication system for SPAs and simple APIs.",
+            "keywords": [
+                "auth",
+                "laravel",
+                "sanctum"
+            ],
+            "support": {
+                "issues": "https://github.com/laravel/sanctum/issues",
+                "source": "https://github.com/laravel/sanctum"
+            },
+            "time": "2026-01-22T22:27:01+00:00"
+        },
         {
             "name": "laravel/serializable-closure",
             "version": "v2.0.7",
diff --git a/config/sanctum.php b/config/sanctum.php
new file mode 100644
index 0000000..44527d6
--- /dev/null
+++ b/config/sanctum.php
@@ -0,0 +1,84 @@
+<?php
+
+use Laravel\Sanctum\Sanctum;
+
+return [
+
+    /*
+    |--------------------------------------------------------------------------
+    | Stateful Domains
+    |--------------------------------------------------------------------------
+    |
+    | Requests from the following domains / hosts will receive stateful API
+    | authentication cookies. Typically, these should include your local
+    | and production domains which access your API via a frontend SPA.
+    |
+    */
+
+    'stateful' => explode(',', env('SANCTUM_STATEFUL_DOMAINS', sprintf(
+        '%s%s',
+        'localhost,localhost:3000,127.0.0.1,127.0.0.1:8000,::1',
+        Sanctum::currentApplicationUrlWithPort(),
+        // Sanctum::currentRequestHost(),
+    ))),
+
+    /*
+    |--------------------------------------------------------------------------
+    | Sanctum Guards
+    |--------------------------------------------------------------------------
+    |
+    | This array contains the authentication guards that will be checked when
+    | Sanctum is trying to authenticate a request. If none of these guards
+    | are able to authenticate the request, Sanctum will use the bearer
+    | token that's present on an incoming request for authentication.
+    |
+    */
+
+    'guard' => ['web'],
+
+    /*
+    |--------------------------------------------------------------------------
+    | Expiration Minutes
+    |--------------------------------------------------------------------------
+    |
+    | This value controls the number of minutes until an issued token will be
+    | considered expired. This will override any values set in the token's
+    | "expires_at" attribute, but first-party sessions are not affected.
+    |
+    */
+
+    'expiration' => null,
+
+    /*
+    |--------------------------------------------------------------------------
+    | Token Prefix
+    |--------------------------------------------------------------------------
+    |
+    | Sanctum can prefix new tokens in order to take advantage of numerous
+    | security scanning initiatives maintained by open source platforms
+    | that notify developers if they commit tokens into repositories.
+    |
+    | See: https://docs.github.com/en/code-security/secret-scanning/about-secret-scanning
+    |
+    */
+
+    'token_prefix' => env('SANCTUM_TOKEN_PREFIX', ''),
+
+    /*
+    |--------------------------------------------------------------------------
+    | Sanctum Middleware
+    |--------------------------------------------------------------------------
+    |
+    | When authenticating your first-party SPA with Sanctum you may need to
+    | customize some of the middleware Sanctum uses while processing the
+    | request. You may change the middleware listed below as required.
+    |
+    */
+
+    'middleware' => [
+        'authenticate_session' => Laravel\Sanctum\Http\Middleware\AuthenticateSession::class,
+        'encrypt_cookies' => Illuminate\Cookie\Middleware\EncryptCookies::class,
+        'validate_csrf_token' => Illuminate\Foundation\Http\Middleware\ValidateCsrfToken::class,
+    ],
+
+];
diff --git a/database/migrations/2026_01_16_152857_create_activity_log_table.php b/database/migrations/2026_01_16_152857_create_activity_log_table.php
index 7c05bc8..945796d 100644
--- a/database/migrations/2026_01_16_152857_create_activity_log_table.php
+++ b/database/migrations/2026_01_16_152857_create_activity_log_table.php
@@ -4,7 +4,7 @@ use Illuminate\Support\Facades\Schema;
 use Illuminate\Database\Schema\Blueprint;
 use Illuminate\Database\Migrations\Migration;
 
-class CreateActivityLogTable extends Migration
+return new class extends Migration
 {
     public function up()
     {
@@ -24,4 +24,4 @@ class CreateActivityLogTable extends Migration
     {
         Schema::connection(config('activitylog.database_connection'))->dropIfExists(config('activitylog.table_name'));
     }
-}
+};
diff --git a/database/migrations/2026_01_16_152858_add_event_column_to_activity_log_table.php b/database/migrations/2026_01_16_152858_add_event_column_to_activity_log_table.php
index 7b797fd..16b7964 100644
--- a/database/migrations/2026_01_16_152858_add_event_column_to_activity_log_table.php
+++ b/database/migrations/2026_01_16_152858_add_event_column_to_activity_log_table.php
@@ -4,7 +4,7 @@ use Illuminate\Support\Facades\Schema;
 use Illuminate\Database\Schema\Blueprint;
 use Illuminate\Database\Migrations\Migration;
 
-class AddEventColumnToActivityLogTable extends Migration
+return new class extends Migration
 {
     public function up()
     {
@@ -19,4 +19,4 @@ class AddEventColumnToActivityLogTable extends Migration
             $table->dropColumn('event');
         });
     }
-}
+};
diff --git a/database/migrations/2026_01_16_152859_add_batch_uuid_column_to_activity_log_table.php b/database/migrations/2026_01_16_152859_add_batch_uuid_column_to_activity_log_table.php
index 8f7db66..85d4025 100644
--- a/database/migrations/2026_01_16_152859_add_batch_uuid_column_to_activity_log_table.php
+++ b/database/migrations/2026_01_16_152859_add_batch_uuid_column_to_activity_log_table.php
@@ -4,7 +4,7 @@ use Illuminate\Support\Facades\Schema;
 use Illuminate\Database\Schema\Blueprint;
 use Illuminate\Database\Migrations\Migration;
 
-class AddBatchUuidColumnToActivityLogTable extends Migration
+return new class extends Migration
 {
     public function up()
     {
@@ -19,4 +19,4 @@ class AddBatchUuidColumnToActivityLogTable extends Migration
             $table->dropColumn('batch_uuid');
         });
     }
-}
+};
diff --git a/database/migrations/tenant/2026_01_16_152857_create_activity_log_table.php b/database/migrations/tenant/2026_01_16_152857_create_activity_log_table.php
index 7c05bc8..945796d 100644
--- a/database/migrations/tenant/2026_01_16_152857_create_activity_log_table.php
+++ b/database/migrations/tenant/2026_01_16_152857_create_activity_log_table.php
@@ -4,7 +4,7 @@ use Illuminate\Support\Facades\Schema;
 use Illuminate\Database\Schema\Blueprint;
 use Illuminate\Database\Migrations\Migration;
 
-class CreateActivityLogTable extends Migration
+return new class extends Migration
 {
     public function up()
     {
@@ -24,4 +24,4 @@ class CreateActivityLogTable extends Migration
     {
         Schema::connection(config('activitylog.database_connection'))->dropIfExists(config('activitylog.table_name'));
     }
-}
+};
diff --git a/database/migrations/tenant/2026_01_16_152858_add_event_column_to_activity_log_table.php b/database/migrations/tenant/2026_01_16_152858_add_event_column_to_activity_log_table.php
index 7b797fd..16b7964 100644
--- a/database/migrations/tenant/2026_01_16_152858_add_event_column_to_activity_log_table.php
+++ b/database/migrations/tenant/2026_01_16_152858_add_event_column_to_activity_log_table.php
@@ -4,7 +4,7 @@ use Illuminate\Support\Facades\Schema;
 use Illuminate\Database\Schema\Blueprint;
 use Illuminate\Database\Migrations\Migration;
 
-class AddEventColumnToActivityLogTable extends Migration
+return new class extends Migration
 {
     public function up()
     {
@@ -19,4 +19,4 @@ class AddEventColumnToActivityLogTable extends Migration
             $table->dropColumn('event');
         });
     }
-}
+};
diff --git a/database/migrations/tenant/2026_01_16_152859_add_batch_uuid_column_to_activity_log_table.php b/database/migrations/tenant/2026_01_16_152859_add_batch_uuid_column_to_activity_log_table.php
index 8f7db66..85d4025 100644
--- a/database/migrations/tenant/2026_01_16_152859_add_batch_uuid_column_to_activity_log_table.php
+++ b/database/migrations/tenant/2026_01_16_152859_add_batch_uuid_column_to_activity_log_table.php
@@ -4,7 +4,7 @@ use Illuminate\Support\Facades\Schema;
 use Illuminate\Database\Schema\Blueprint;
 use Illuminate\Database\Migrations\Migration;
 
-class AddBatchUuidColumnToActivityLogTable extends Migration
+return new class extends Migration
 {
     public function up()
     {
@@ -19,4 +19,4 @@ class AddBatchUuidColumnToActivityLogTable extends Migration
             $table->dropColumn('batch_uuid');
         });
     }
-}
+};
diff --git a/database/migrations/tenant/2026_02_06_101512_create_personal_access_tokens_table.php b/database/migrations/tenant/2026_02_06_101512_create_personal_access_tokens_table.php
new file mode 100644
index 0000000..40ff706
--- /dev/null
+++ b/database/migrations/tenant/2026_02_06_101512_create_personal_access_tokens_table.php
@@ -0,0 +1,33 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::create('personal_access_tokens', function (Blueprint $table) {
+            $table->id();
+            $table->morphs('tokenable');
+            $table->text('name');
+            $table->string('token', 64)->unique();
+            $table->text('abilities')->nullable();
+            $table->timestamp('last_used_at')->nullable();
+            $table->timestamp('expires_at')->nullable()->index();
+            $table->timestamps();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('personal_access_tokens');
+    }
+};
diff --git a/database/migrations/tenant/2026_02_06_102000_add_external_pos_id_to_products_table.php b/database/migrations/tenant/2026_02_06_102000_add_external_pos_id_to_products_table.php
new file mode 100644
index 0000000..7d9315f
--- /dev/null
+++ b/database/migrations/tenant/2026_02_06_102000_add_external_pos_id_to_products_table.php
@@ -0,0 +1,28 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::table('products', function (Blueprint $table) {
+            $table->string('external_pos_id')->nullable()->after('id')->index();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('products', function (Blueprint $table) {
+            $table->dropColumn('external_pos_id');
+        });
+    }
+};
diff --git a/database/migrations/tenant/2026_02_06_102100_create_sales_orders_tables.php b/database/migrations/tenant/2026_02_06_102100_create_sales_orders_tables.php
new file mode 100644
index 0000000..709e592
--- /dev/null
+++ b/database/migrations/tenant/2026_02_06_102100_create_sales_orders_tables.php
@@ -0,0 +1,45 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::create('sales_orders', function (Blueprint $table) {
+            $table->id();
+            $table->string('external_order_id')->nullable()->unique();
+            $table->string('status')->default('completed');
+            $table->string('payment_method')->nullable();
+            $table->decimal('total_amount', 12, 4)->default(0);
+            $table->timestamp('sold_at')->useCurrent();
+            $table->json('raw_payload')->nullable();
+            $table->timestamps();
+        });
+
+        Schema::create('sales_order_items', function (Blueprint $table) {
+            $table->id();
+            $table->foreignId('sales_order_id')->constrained('sales_orders')->cascadeOnDelete();
+            $table->foreignId('product_id')->nullable()->constrained('products')->nullOnDelete();
+            $table->string('product_name');
+            $table->decimal('quantity', 12, 4);
+            $table->decimal('price', 12, 4);
+            $table->decimal('total', 12, 4);
+            $table->timestamps();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('sales_order_items');
+        Schema::dropIfExists('sales_orders');
+    }
+};
diff --git a/database/migrations/tenant/2026_02_06_103718_add_sku_to_products_table.php b/database/migrations/tenant/2026_02_06_103718_add_sku_to_products_table.php
new file mode 100644
index 0000000..2412a2a
--- /dev/null
+++ b/database/migrations/tenant/2026_02_06_103718_add_sku_to_products_table.php
@@ -0,0 +1,28 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::table('products', function (Blueprint $table) {
+            $table->string('sku')->nullable()->after('barcode')->comment('SKU');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('products', function (Blueprint $table) {
+            $table->dropColumn(['sku']);
+        });
+    }
+};
diff --git a/resources/js/Pages/Landlord/Tenant/Show.tsx b/resources/js/Pages/Landlord/Tenant/Show.tsx
index c4ceaad..8f8ef00 100644
--- a/resources/js/Pages/Landlord/Tenant/Show.tsx
+++ b/resources/js/Pages/Landlord/Tenant/Show.tsx
@@ -19,16 +19,44 @@ interface Tenant {
     domains: Domain[];
 }
 
-interface Props {
-    tenant: Tenant;
+interface Token {
+    id: number;
+    name: string;
+    last_used_at: string;
+    created_at: string;
 }
 
-export default function TenantShow({ tenant }: Props) {
+interface Flash {
+    success: string | null;
+    error: string | null;
+    new_token: string | null;
+}
+
+interface Props {
+    tenant: Tenant;
+    tokens: Token[];
+    flash: Flash;
+}
+
+export default function TenantShow({ tenant, tokens = [], flash }: Props) {
     const [showAddDomain, setShowAddDomain] = useState(false);
+    const [showAddToken, setShowAddToken] = useState(false);
+
     const { data, setData, post, processing, errors, reset } = useForm({
         domain: "",
     });
 
+    // Token Form
+    const {
+        data: tokenData,
+        setData: setTokenData,
+        post: postToken,
+        processing: processingToken,
+        reset: resetToken
+    } = useForm({
+        name: "",
+    });
+
     const handleAddDomain = (e: FormEvent) => {
         e.preventDefault();
         post(route("landlord.tenants.domains.store", tenant.id), {
@@ -39,6 +67,24 @@ export default function TenantShow({ tenant }: Props) {
         });
     };
 
+    const handleAddToken = (e: FormEvent) => {
+        e.preventDefault();
+        postToken(route("landlord.tenants.tokens.store", tenant.id), {
+            onSuccess: () => {
+                resetToken();
+                // Don't close immediately if we want to show flash message? 
+                // Flash message usually appears on redirect back.
+                setShowAddToken(false);
+            },
+        });
+    };
+
+    const handleRevokeToken = (tokenId: number) => {
+        if (confirm("確定要撤銷此金鑰嗎？撤銷後無法復原，POS 連線將中斷。")) {
+            router.delete(route("landlord.tenants.tokens.destroy", [tenant.id, tokenId]));
+        }
+    };
+
     const handleRemoveDomain = (domainId: number) => {
         if (confirm("確定要移除這個域名嗎？")) {
             router.delete(route("landlord.tenants.domains.destroy", [tenant.id, domainId]));
@@ -174,6 +220,84 @@ export default function TenantShow({ tenant }: Props) {
                         </ul>
                     )}
                 </div>
+
+                {/* API Tokens Card */}
+                <div className="bg-white rounded-xl border border-slate-200 p-6">
+                    <div className="flex items-center justify-between mb-4">
+                        <h2 className="text-lg font-semibold text-slate-900">API 金鑰 (POS 整合)</h2>
+                        <button
+                            onClick={() => setShowAddToken(!showAddToken)}
+                            className="text-primary-main hover:text-primary-dark flex items-center gap-1 text-sm"
+                        >
+                            <Plus className="w-4 h-4" />
+                            新增金鑰
+                        </button>
+                    </div>
+
+                    {flash?.new_token && (
+                        <div className="mb-4 p-4 bg-green-50 border border-green-200 rounded-lg">
+                            <p className="text-sm text-green-800 font-bold mb-1">金鑰建立成功！請立即複製，離開後將無法再次查看。</p>
+                            <div className="flex items-center gap-2">
+                                <code className="flex-1 bg-white px-2 py-1 rounded border border-green-200 text-sm break-all font-mono select-all">
+                                    {flash.new_token}
+                                </code>
+                            </div>
+                        </div>
+                    )}
+
+                    {showAddToken && (
+                        <form onSubmit={handleAddToken} className="mb-4 flex gap-2">
+                            <input
+                                type="text"
+                                value={tokenData.name}
+                                onChange={(e) => setTokenData("name", e.target.value)}
+                                placeholder="金鑰名稱 (例如: POS-01)"
+                                className="flex-1 px-4 py-2 border border-slate-300 rounded-lg focus:ring-2 focus:ring-primary-main focus:border-primary-main"
+                            />
+                            <button
+                                type="submit"
+                                disabled={processingToken}
+                                className="bg-primary-main hover:bg-primary-dark text-white px-4 py-2 rounded-lg disabled:opacity-50"
+                            >
+                                建立
+                            </button>
+                        </form>
+                    )}
+
+                    {tokens.length === 0 ? (
+                        <p className="text-slate-500 text-sm">尚未建立任何 API 金鑰</p>
+                    ) : (
+                        <div className="overflow-x-auto">
+                            <table className="w-full text-sm text-left">
+                                <thead className="text-xs text-slate-500 uppercase bg-slate-50">
+                                    <tr>
+                                        <th className="px-3 py-2">名稱</th>
+                                        <th className="px-3 py-2">建立時間</th>
+                                        <th className="px-3 py-2">最後使用</th>
+                                        <th className="px-3 py-2 text-right">操作</th>
+                                    </tr>
+                                </thead>
+                                <tbody>
+                                    {tokens.map((token) => (
+                                        <tr key={token.id} className="border-b border-slate-100 last:border-0 hover:bg-slate-50">
+                                            <td className="px-3 py-2 font-medium text-slate-900">{token.name}</td>
+                                            <td className="px-3 py-2 text-slate-500">{token.created_at}</td>
+                                            <td className="px-3 py-2 text-slate-500">{token.last_used_at}</td>
+                                            <td className="px-3 py-2 text-right">
+                                                <button
+                                                    onClick={() => handleRevokeToken(token.id)}
+                                                    className="text-red-600 hover:text-red-900 hover:underline"
+                                                >
+                                                    撒銷
+                                                </button>
+                                            </td>
+                                        </tr>
+                                    ))}
+                                </tbody>
+                            </table>
+                        </div>
+                    )}
+                </div>
             </div>
         </LandlordLayout>
     );
diff --git a/routes/landlord.php b/routes/landlord.php
index 67ebd71..2d421b9 100644
--- a/routes/landlord.php
+++ b/routes/landlord.php
@@ -34,4 +34,8 @@ Route::prefix('landlord')->name('landlord.')->middleware(['web', 'auth', \App\Ht
     // 租戶樣式管理
     Route::get('tenants/{tenant}/branding', [TenantController::class, 'showBranding'])->name('tenants.branding');
     Route::post('tenants/{tenant}/branding', [TenantController::class, 'updateBranding'])->name('tenants.branding.update');
+
+    // 租戶 API Token 管理
+    Route::post('tenants/{tenant}/tokens', [TenantController::class, 'createToken'])->name('tenants.tokens.store');
+    Route::delete('tenants/{tenant}/tokens/{token}', [TenantController::class, 'revokeToken'])->name('tenants.tokens.destroy');
 });
diff --git a/tests/Feature/Integration/PosApiTest.php b/tests/Feature/Integration/PosApiTest.php
new file mode 100644
index 0000000..38b3f04
--- /dev/null
+++ b/tests/Feature/Integration/PosApiTest.php
@@ -0,0 +1,202 @@
+<?php
+
+namespace Tests\Feature\Integration;
+
+use Tests\TestCase;
+use App\Modules\Core\Models\Tenant;
+use App\Modules\Core\Models\User;
+use App\Modules\Inventory\Models\Product;
+use App\Modules\Integration\Models\SalesOrder;
+use Illuminate\Support\Facades\DB;
+use Stancl\Tenancy\Facades\Tenancy;
+
+class PosApiTest extends TestCase
+{
+    // Use RefreshDatabase to reset DB state. 
+    // Note: In Tenancy, this usually resets Central DB. 
+    // For Tenant DBs, we heavily rely on Stancl's behavior or need to act carefully.
+    // For now, assume we can create a tenant and its DB will be migrated or accessible.
+    
+    protected $tenant;
+    protected $user;
+    protected $token;
+    protected $domain;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        
+        \Artisan::call('migrate:fresh'); // Force fresh DB for isolation without RefreshDatabase trait
+        
+        $this->domain = 'test-' . \Illuminate\Support\Str::random(8) . '.erp.local';
+        $tenantId = 'test_tenant_' . \Illuminate\Support\Str::random(8);
+
+        // Ensure we are in central context
+        tenancy()->central(function () use ($tenantId) {
+             // Create a tenant
+            $this->tenant = Tenant::create([
+                'id' => $tenantId,
+                'name' => 'Test Tenant',
+            ]);
+            
+            $this->tenant->domains()->create(['domain' => $this->domain]);
+        });
+
+        // Initialize to create User and Token
+        tenancy()->initialize($this->tenant);
+        
+        \Artisan::call('tenants:migrate');
+
+        $this->user = User::factory()->create([
+            'email' => 'admin@test.local',
+            'name' => 'Admin',
+        ]);
+        
+        $this->token = $this->user->createToken('POS-Test-Token')->plainTextToken;
+        
+        $category = \App\Modules\Inventory\Models\Category::create(['name' => 'General', 'code' => 'GEN']);
+
+        // Create a product for testing
+        Product::create([
+            'name' => 'Existing Product',
+            'code' => 'P-001',
+            'external_pos_id' => 'EXT-001',
+            'sku' => 'SKU-001',
+            'price' => 100,
+            'is_active' => true,
+            'category_id' => $category->id,
+        ]);
+        
+        // End tenancy initialization to simulate external request
+        tenancy()->end();
+    }
+
+    protected function tearDown(): void
+    {
+        if ($this->tenant) {
+            $this->tenant->delete();
+        }
+        parent::tearDown();
+    }
+    
+    public function test_upsert_product_creates_new_product()
+    {
+        \Laravel\Sanctum\Sanctum::actingAs($this->user, ['*']);
+
+        $payload = [
+            'external_pos_id' => 'EXT-NEW-002',
+            'name' => 'New Product',
+            'price' => 200,
+            'sku' => 'SKU-NEW',
+        ];
+
+        $response = $this->withHeaders([
+            'X-Tenant-Domain' => $this->domain,
+            'Accept' => 'application/json',
+        ])->postJson('/api/v1/integration/products/upsert', $payload);
+
+        $response->assertStatus(200)
+                 ->assertJsonPath('message', 'Product synced successfully');
+
+        // Verify in Tenant DB
+        tenancy()->initialize($this->tenant);
+        $this->assertDatabaseHas('products', [
+            'external_pos_id' => 'EXT-NEW-002',
+            'name' => 'New Product',
+        ]);
+        tenancy()->end();
+    }
+
+    public function test_upsert_product_updates_existing_product()
+    {
+        \Laravel\Sanctum\Sanctum::actingAs($this->user, ['*']);
+
+        $payload = [
+            'external_pos_id' => 'EXT-001',
+            'name' => 'Updated Name',
+            'price' => 150,
+        ];
+
+        $response = $this->withHeaders([
+            'X-Tenant-Domain' => $this->domain,
+            'Accept' => 'application/json',
+        ])->postJson('/api/v1/integration/products/upsert', $payload);
+
+        $response->assertStatus(200);
+
+        tenancy()->initialize($this->tenant);
+        $this->assertDatabaseHas('products', [
+            'external_pos_id' => 'EXT-001',
+            'name' => 'Updated Name',
+            'price' => 150,
+        ]);
+        tenancy()->end();
+    }
+
+    public function test_create_order_deducts_inventory()
+    {
+        // Setup inventory first
+        tenancy()->initialize($this->tenant);
+        $product = Product::where('external_pos_id', 'EXT-001')->first();
+        
+        // We need a warehouse
+        $warehouse = \App\Modules\Inventory\Models\Warehouse::create(['name' => 'Main Warehouse', 'code' => 'MAIN']);
+        
+        // Add initial stock
+        \App\Modules\Inventory\Models\Inventory::create([
+            'product_id' => $product->id,
+            'warehouse_id' => $warehouse->id,
+            'quantity' => 100,
+            'batch_number' => 'BATCH-TEST-001',
+            'arrival_date' => now()->toDateString(),
+            'origin_country' => 'TW',
+        ]);
+        
+        $warehouseId = $warehouse->id;
+        tenancy()->end();
+
+        \Laravel\Sanctum\Sanctum::actingAs($this->user, ['*']);
+
+        $payload = [
+            'external_order_id' => 'ORD-001',
+            'warehouse_id' => $warehouseId,
+            'sold_at' => now()->toIso8601String(),
+            'items' => [
+                [
+                    'pos_product_id' => 'EXT-001',
+                    'qty' => 5,
+                    'price' => 100
+                ]
+            ]
+        ];
+
+        $response = $this->withHeaders([
+            'X-Tenant-Domain' => $this->domain,
+            'Accept' => 'application/json',
+        ])->postJson('/api/v1/integration/orders', $payload);
+
+        $response->assertStatus(201)
+                 ->assertJsonPath('message', 'Order synced and stock deducted successfully');
+
+        // Verify Order and Inventory
+        tenancy()->initialize($this->tenant);
+        
+        $this->assertDatabaseHas('sales_orders', [
+            'external_order_id' => 'ORD-001',
+        ]);
+        
+        $this->assertDatabaseHas('sales_order_items', [
+            'product_id' => $product->id, // We need to fetch ID again or rely on correct ID
+            'quantity' => 5,
+        ]);
+        
+        // Verify stock deducted: 100 - 5 = 95
+        $this->assertDatabaseHas('inventories', [
+            'product_id' => $product->id,
+            'warehouse_id' => $warehouseId,
+            'quantity' => 95,
+        ]);
+        
+        tenancy()->end();
+    }
+}