HELP!... Custom Domain Checker

I've just followed the instruction on this page http://docs.whmcs.com/Creating_Pages

• Do I've copied and renamed the domainchecker.tpl file to customdc.tpl
• Created my custom.php file in the root of our install.
• Edited the $ca->setTemplate('customdc'); line in the custom.php file

Goto page http://myaccount.lanquest-hosting.net/custom.php
The page loads and looks ok. But when I click the "Search Multiple TLDs", it's empty :(

I can see it's possible here https://ipgeek.co.uk/domainchecker.php.

But how?... What am I missing or doing wrong?
I hope someone can shed some light on this as I've spent loads of hours searching without success.

Much appreciated in advance.