fix bug of free products from pos in update

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

@@ -14,8 +14,11 @@ class POSFreeProductSerializer(serializers.ModelSerializer):
         """
         @check free product for pos to be unique
         """
-        organization = attrs['organization']
+
+        if not self.instance:
+
             product = attrs['product']
+            organization = attrs['organization']
 
             if self.Meta.model.objects.filter(organization=organization, product=product).exists():
                 raise FreePOSProductUniqueCheck()