1. Locate whmcs installation directory on your server
2. Create vesta directory in the modules/server subdirectory
3. Download php module
wget http://c.vestacp.com/0.9.8/rhel/whmcs-module.php -O vesta.php
The WHMCS plugin allows managing servers running Vesta Control Panel. You can automatically create delete or suspend user accounts. Users are able to change passwords and manage their web/mail/DNS domains.