Error: License validation failed
This error occurs when you have already used a license for the same product on the same server. For example, when you use a newly purchased license after a trial, the license configuration file might not get updated with the new license.
Solution : As a fix, if you have SSH access to your server, all that you need to do .
If you are a sudo user, run
sudo bash -c 'echo > /usr/local/psa/var/modules/rkhunter/license.conf'
If you are a root user, the command should be
echo > /usr/local/psa/var/modules/rkhunter/license.conf
Apply the new license once again on the Plugin Interface in your Plesk panel, and it should work.
If you are having trouble doing this yourself, please contact us here.