I looked at your account.
You have a server (watch43) which had several certificate error problems.
(you had used up your quota of certificates in very short order).
I reset the certificate for you.
Please restart the server and see if it can now sign into your account.
Be advised, if you’re using your FQDN to access Plex, you must also add the cert to PMS for it to work correctly.
The cert P12 must include the Key, Cert, and CA for PMS to accept it (when PMS starts)
Given OpenSSLv3 is now the standard, you need to take this into consideration when generating your cert.