diff --git a/app/Domains/Cart/Middleware/MergeGuestCartMiddleware.php b/app/Domains/Cart/Middleware/MergeGuestCartMiddleware.php
new file mode 100644
index 0000000..e36a265
--- /dev/null
+++ b/app/Domains/Cart/Middleware/MergeGuestCartMiddleware.php
@@ -0,0 +1,73 @@
+<?php
+
+namespace App\Domains\Cart\Middleware;
+
+use App\Domains\Cart\Models\Cart;
+use App\Domains\Tenant\Models\Tenant;
+use Closure;
+use Illuminate\Http\Request;
+use Illuminate\Support\Facades\Auth;
+use Illuminate\Support\Facades\Cookie;
+use Symfony\Component\HttpFoundation\Response;
+
+class MergeGuestCartMiddleware
+{
+    public function handle(Request $request, Closure $next): Response
+    {
+        $guestToken = $request->cookie('guest_token');
+
+        // Resolve authenticated user optionally (from default guard or sanctum guard)
+        $user = $request->user() ?? Auth::guard('sanctum')->user();
+        $userId = $user?->getKey();
+
+        \Illuminate\Support\Facades\Log::info('MergeGuestCartMiddleware processed', [
+            'user_id' => $userId,
+            'guest_token' => $guestToken,
+        ]);
+
+        if ($user !== null && is_string($guestToken) && $guestToken !== '') {
+            $tenantParam = $request->route('tenant');
+            $tenantCodigo = null;
+
+            if ($tenantParam instanceof Tenant) {
+                $tenantCodigo = $tenantParam->codigo;
+            } elseif (is_string($tenantParam)) {
+                $tenantCodigo = $tenantParam;
+            }
+
+            if ($tenantCodigo !== null) {
+                $guestCart = Cart::query()
+                    ->where('tenant_codigo', $tenantCodigo)
+                    ->where('guest_token', $guestToken)
+                    ->first();
+
+                if ($guestCart !== null && $guestCart->items()->exists()) {
+                    $userCart = Cart::query()
+                        ->where('tenant_codigo', $tenantCodigo)
+                        ->where('user_id', $userId)
+                        ->first();
+
+                    if ($userCart !== null) {
+                        $userCart->delete();
+                    }
+
+                    $guestCart->update([
+                        'user_id' => $userId,
+                        'guest_token' => null,
+                    ]);
+                }
+            }
+        }
+
+        $response = $next($request);
+
+        if ($user !== null && is_string($guestToken) && $guestToken !== '') {
+            // Remove the cookie from the response since the user is authenticated.
+            if (method_exists($response, 'withCookie')) {
+                $response->withCookie(Cookie::forget('guest_token'));
+            }
+        }
+
+        return $response;
+    }
+}
diff --git a/app/Domains/Cart/Services/CartService.php b/app/Domains/Cart/Services/CartService.php
index 3bacb13..a814fcf 100644
--- a/app/Domains/Cart/Services/CartService.php
+++ b/app/Domains/Cart/Services/CartService.php
@@ -104,7 +104,7 @@ class CartService
      */
     protected function resolveIdentity(Request $request, bool $generateGuestToken = false): ?array
     {
-        $user = $request->user();
+        $user = $request->user() ?? \Illuminate\Support\Facades\Auth::guard('sanctum')->user();
 
         if ($user instanceof User) {
             return [
diff --git a/app/Domains/Cart/routes/api.php b/app/Domains/Cart/routes/api.php
index 20300ae..910a331 100644
--- a/app/Domains/Cart/routes/api.php
+++ b/app/Domains/Cart/routes/api.php
@@ -3,9 +3,11 @@
 use App\Domains\Cart\Controllers\CartController;
 use Illuminate\Support\Facades\Route;
 
-Route::prefix('tenants/{tenant:codigo}')->group(function (): void {
-    Route::get('cart', [CartController::class, 'show']);
-    Route::post('cart/items', [CartController::class, 'addItem']);
-    Route::patch('cart/items/{productVariant}', [CartController::class, 'updateItemQuantity']);
-    Route::delete('cart/items/{productVariant}', [CartController::class, 'removeItem']);
-});
+Route::prefix('tenants/{tenant:codigo}')
+    ->middleware(\App\Domains\Cart\Middleware\MergeGuestCartMiddleware::class)
+    ->group(function (): void {
+        Route::get('cart', [CartController::class, 'show']);
+        Route::post('cart/items', [CartController::class, 'addItem']);
+        Route::patch('cart/items/{productVariant}', [CartController::class, 'updateItemQuantity']);
+        Route::delete('cart/items/{productVariant}', [CartController::class, 'removeItem']);
+    });