diff --git a/uncloud/uncloud_pay/models.py b/uncloud/uncloud_pay/models.py
index 32d3eac..17afbcb 100644
--- a/uncloud/uncloud_pay/models.py
+++ b/uncloud/uncloud_pay/models.py
@@ -182,7 +182,7 @@ class Bill(models.Model):
 
     @property
     def reference(self):
-        return "{}_{}".format(
+        return "{}-{}".format(
                 self.owner.username,
                 self.creation_date.strftime("%Y-%m-%d-%H%M"))