there comes a time when you should give up. but you dont

synapse/http/matrixfederationclient.py

@@ -707,7 +707,7 @@ class MatrixFederationHttpClient(object):
         }
 
         response = yield self._send_request_with_optional_trailing_slash(
-            request, try_trailing_slash_on_400, send_request_args,
+            request, try_trailing_slash_on_400, backoff_on_404, send_request_args,
         )
 
         body = yield _handle_json_response(