SERVER_ERROR NO: 51 MSG: User token not found

Hello, @soulpearl.

Please, re-install the CleanTalk Security Plugin with the Complete Deactivation option:
• WordPress Admin Page —> Settings —> Security by CleanTalk —> General Settings —> enable “Complete Deactivation” —> Save Changes;
• Plugins —> Installed plugins —> Security by CleanTalk —> Deactivate and Delete.

Then install it anew:
https://cleantalk.org/help/install-wordpress-security

It will solve the issue. Did it help?

Happy to help, @soulpearl!
All the best.