fix bug of free products from pos in update

apps/product/pos/api/v1/serializers/product_serializers.py

@@ -14,11 +14,14 @@ class POSFreeProductSerializer(serializers.ModelSerializer):
         """
         @check free product for pos to be unique
         """
-        organization = attrs['organization']
-        product = attrs['product']
 
-        if self.Meta.model.objects.filter(organization=organization, product=product).exists():
-            raise FreePOSProductUniqueCheck()
+        if not self.instance:
+
+            product = attrs['product']
+            organization = attrs['organization']
+
+            if self.Meta.model.objects.filter(organization=organization, product=product).exists():
+                raise FreePOSProductUniqueCheck()
 
         return attrs