Are you using two factor authentication ? PlexConnect does not supports it, but I think that you can still login following this procedure
Old Third-Party Apps & Tools
In the very rare case where you’re using a Plex app that doesn’t directly support 2FA verification (which typically means it’s a third-party app or tool that isn’t using our standard authentication methods), you can still sign in via 2FA. Specifically, you append a valid verification code to the end of the password when submitting: <password><verification code>
For instance, imagine that your password is “secret” (please, please use a strong, unique password) and that you check your authenticator app and receive the verification code “123456”. You would then submit secret123456 as the password.
Thanks for replying so fast but I don’t use plex 2fa. I don’t know what the problem is but my best guess would be a mistake in setting up the files on my mac.