Link goes to home page

I've used the WHMCS URL Encoder, but all my products are linking directly to the home page.

This is the original link;
http://www.moonworks.co.uk/store/cart.php?a=add&pid=15

This is the encoded link:
http://www.moonworks.co.uk/?whmcsportalpage=whmcs%3A%2F%2Fwww.moonworks.co.uk%2Fstore%2Fcart.php%3Fa%3Dadd%26pid%3D15