Invites are now working.

Signed-off-by: Cliff Hill <clifford.hill@gsa.gov>

app/notify_client/user_api_client.py

@@ -168,7 +168,7 @@ class UserApiClient(NotifyAdminAPIClient):
     @cache.delete("user-{user_id}")
     def add_user_to_service(self, service_id, user_id, permissions, folder_permissions):
         # permissions passed in are the combined UI permissions, not DB permissions
-        endpoint = "/service/{}/users/{}".format(service_id, user_id)
+        endpoint = f"/service/{service_id}/users/{user_id}"
         data = {
             "permissions": [
                 {"permission": x}