Google Script app code

function createTicket(e) {

  var API_KEY='My API ';

  var ENDPOINT = 'My domain'; // change to https if SSL is configured.

  var headers = {
    'Content-type': 'application/json',
    'Authorization': 'Basic ' + Utilities.base64Encode(API_KEY + ':X')
  };


  var payload = JSON.stringify({
"description":"Help needed desparately",
"subject":"Testing API",
"email":"[email protected]",
"priority":1,
"status": 2 ,
/*I did try this didn't work either*/
// 'custom_field[cf_campus]':'QLD'
"custom_field": 
{
       "cf_campus": "QLD"

    }
})



  var url = ENDPOINT + '/api/v2/tickets';

  var options = {
    'method': 'post',
    'headers': headers,
    'payload': payload,
    muteHttpExceptions: true
  };
  // Logger.log("url: " + url);
  Logger.log("payload: " + options.payload);
  Logger.log("headers: " + options.headers);
  var response = UrlFetchApp.fetch(url, options);

  Logger.log("code: " + response.getResponseCode());
  Logger.log("text: " + response.getContentText());
}

/* Getting this error in output
code: 400
text: {"description":"Validation failed","errors":[{"field":"custom_field","message":"Unexpected/invalid field in request","code":"invalid_field"}]}
*/

getting error 400

text: {"description":"Validation failed","errors":[{"field":"custom_field","message":"Unexpected/invalid field in request","code":"invalid_field"}]}