You can try to force the cert to refresh. Stop plex, go to the Cache directory in the Plex Media Server folder, remove (don’t delete) the *.p12 file, and start plex back up. It should download a new cert.
The 429 error would require someone from Plex or one of the mods that has access to reset the cert of remove the rate limit (if that’s possible), otherwise you have to wait for the rate limit to be lifted.
I’m not sure..but you can shut the server down so it doesn’t keep trying. Confirm there are no permissions issues that may be causing your server to keep getting unclaimed/request a new cert
@BigWheel anything you can do to remove the rate limit, or is it best to wait it out?