Liberty Reserve's website can be visited @ www.libertyreserve.com
Configuring the module in WHMCS is pretty straightforward. Just activate the Liberty Reserve module in Setup > Payment Gateways as normal and then enter your Account Number, Store Name and Secret Key where requested.
The Secret Key is a code which you obtain from within your Liberty Reserve account in order to verify callbacks are genuine.
Also within your Liberty Reserve control panel, you should set the callback urls as follows in order for your customers to be returned to your site and invoices to automatically get marked paid:
Success URL: http://www.yourdomain.com/whmcs/clientarea.php Fail URL: http://www.yourdomain.com/whmcs/ Status URL: http://www.yourdomain.com/whmcs/modules/gateways/callback/libertyreserve.php
Redirect HTTP method should be set to POST for both return data types.