Apps Script: Exception: Request failed for ... returned code 4xx/5xx

UrlFetchApp.fetch throws this exception whenever the remote server answers with an HTTP error status. The request did reach the server and a response came back; the server rejected it. The number after returned code is the HTTP status, and the truncated response is the start of the server's own error body.

The status code tells you where to look. 400 means the request was malformed, 401 and 403 mean authentication or permission problems, 404 means a wrong URL, 429 means you are being rate-limited, and 5xx means the server failed.

Google's documentation says that with muteHttpExceptions: true the fetch does not throw when the response code indicates failure, and instead returns the response so you can read the full status and body.

const res = UrlFetchApp.fetch(url, {
  method: 'post',
  contentType: 'application/json',
  headers: { Authorization: 'Bearer ' + token },
  payload: JSON.stringify(body),
  muteHttpExceptions: true
});
if (res.getResponseCode() >= 400) {
  console.log(res.getResponseCode(), res.getContentText());
}

Wrap every external call in one helper that sets muteHttpExceptions, checks the status, logs failures with the response body, and retries only retryable codes (429 and 5xx) with backoff. Store credentials in script properties and validate them at the start of a run.