diff --git a/uncloud_django_based/uncloud/uncloud_pay/models.py b/uncloud_django_based/uncloud/uncloud_pay/models.py
index b06473e..3b4535c 100644
--- a/uncloud_django_based/uncloud/uncloud_pay/models.py
+++ b/uncloud_django_based/uncloud/uncloud_pay/models.py
@@ -455,9 +455,9 @@ class BillingAddress(models.Model):
     def get_addresses_for(user):
         return BillingAddress.objects.filter(owner=user)
 
-    @staticmethod
-    def get_preferred_address_for(user):
-        addresses = get_addresses_for(user)
+    @classmethod
+    def get_preferred_address_for(cls, user):
+        addresses = cls.get_addresses_for(user)
         if len(addresses) == 0:
             return None
         else:
@@ -927,7 +927,7 @@ class Product(UncloudModel):
             billing_address = BillingAddress.get_preferred_address_for(self.owner)
 
             if not billing_address:
-                raise ValidationError("Cannot create order without a billing address")
+                raise ValidationError("Cannot order without a billing address")
 
             self.order = Order(owner=self.owner,
                                billing_address=billing_address)