How to not accept invalid TLDs with the web20Cart domain checker?

[kristofferR]

I use the Web20Cart on my site, but the domain checker doesn't work adequately.

A demo of how it works on my site can be found here: http://demo.whmcs.com/order/?pid=2

 

You can try entering yahoo.com. It is obviously already taken, but yahoo.yahoo works even though it isn't a valid domain extension.

 

How can I restrict it to only say that domains ending with .com, .net and .org are valid?

[WHMCS John]

Clients have always been able to enter any domain extension they like when choosing the "I will register it myself" option. Implementing this kind of check would involve having to list every single domain extension in existence!