https://www.plesk.com/kb/support/login-to-plesk-from-whmcs-redirects-to-plesk-login-page-instead-of-logging-in/
Login to Plesk from WHMCS redirects to Plesk login page instead of logging in. - Support Cases from...
Symptoms SSO connection to Plesk though WHMCS fails. Login to Plesk from WHMCS redirects to Plesk login page back instead of logging in. WHMCS is behind...
login to plesk