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 Cloudflare,
Cause
User's IP address is changed during a Plesk session. This may happen if user's IP address is dynamic or the domain/hostname which is used as a URL for Plesk is behind Cloudflare.
By default, Plesk does not allow IP address changes during a single session.
Resolution
Allow IP address changes during a single session:
Log in to Plesk (use the server IP address if it is not possible to log in using the hostname).
Go to Tools & Settings > Session Idle Time and enable the option Allow IP address changes during a single session.
Click OK to apply the changes.
Command-line instructions
Connect to the Plesk server via SSH (Linux) / RDP (Windows Server).
Run the following command to enable IP address changes during a single session (on Windows Server, start a command prompt as an Administrator):
# plesk bin settings --set disable_check_session_ip=true
