REST API HTTP response codes REST Messages sent to a ServiceNow instance return a specific HTTP response code. Status Code Message Details 200 Success Success with response body. 201 Created Success with response body. 204 Success Success with no response body. 400 Bad Request The request URI does not match the APIs in the system, or the operation failed for unknown reasons. Invalid headers can also cause this error. 401 Unauthorized The user is not authorized to use the API. 403 Forbidden The requested operation is not permitted for the user. This error can also be caused by ACL failures, or business rule or data policy constraints. 404 Not found The requested resource was not found. This can be caused by an ACL constraint or if the resource does not exist. 405 Method not allowed The HTTP action is not allowed for the requested REST API, or it is not supported by any API. 406 Not acceptable The endpoint does not support the response format specified in the request Accept header. 415 Unsupported media type The endpoint does not support the format of the request body.