It’s not actually a server ID, it’s a certificate UUID; how you find it depends up the host on which you run your Plex Media Server:
- Windows - In Regedit, navigate to
HKEY_CURRENT_USER\SOFTWARE\Plex, Inc.\Plex Media Serverand find the value ofCertificateUUID. - macOS - Run
defaults read com.plexapp.plexmediaserver CertificateUUID. - Linux - Find your
Preferences.xmlfile in your Plex data directory and locate theCertificateUUIDparameter within. - NAS - Generally found in your
Preferences.xml. Where it’s located depends on the NAS.