Forminator Webhook Integration “Failed to process request : Bad Request”

I am setting up a webhook integration to Apps Script that is supposed to add users to a Google Group based on the email information from the Forminator Form. In this process, something changed and when I created a new deployment in Apps Script – updating the link in the Forminator Integration page when trying to add the “Webhook” integration always results in the “Failed to process request : Bad Request” error. The code in the Apps Script (linked to Web App URL) is currently shown below:

function doGet(e) {
  return ContentService.createTextOutput('OK')
    .setMimeType(ContentService.MimeType.TEXT);
}

function doPost(e) {
  return ContentService.createTextOutput('OK')
    .setMimeType(ContentService.MimeType.TEXT);
}

This form previously accepted submissions properly and sent the data to the webhook successfully (as is shown in the logs), but now even the most simple of scripts like I have reverted to using (like the one above) results in this error which does not allow me to setup the integration.

Any help is greatly appreciated.

Cheers, Adam