Add todo

server/oauth/mutations.py

@@ -26,6 +26,7 @@ class Coupon(relay.ClientIDMutation):
             raise Exception('not_authenticated')
 
         try:
+            # todo: differenciate between invalid_coupon and other errors like "delivery_address_not_set"
             response = hep_client.redeem_coupon(coupon_code, hep_id, request=info.context)
         except HepClientException:
             raise Exception('unknown_error')