SendMail OAuth stopped working in FileMaker 20.2.1

Error code 1542

When you try to send a mail using the new OAuth feature of FileMaker, the process is aborted with error 1542 in FileMaker version 20.2.1. The error means, Access token could not be generated successfully.

FileMaker can only solve this internally with an update to a new version, which is not yet available.
This affects both, Microsoft OAuth 2.0 and Google OAuth 2.0

If you use sendmail via OAuth, I would definitely downgrade to FileMaker version 2.1.2.204

Update November 2023

Claris has fixed the issue with version 20.3.1