WHMCS Integration - Domain checker doen't work

Hi,

I've configured WHMCS settings and I can register and login to the client portal but I cannot lookup the domain names here
http://www.oasysclub.com/whmcs/whmcsportal/domainchecker.php/?

For example, I enter the "testtest.com" (or any other) and always see the message "The domain you entered is not valid"

Tell me please, what is the reason?

Regards,
Olga