If you have an Instantcart shop, you can park and un-park one main domain name ontop of your account via the Instantcart webservices panel. Please note that you can only park a domain name once you have setup your web shop using the “Setup my Site” button.
You may have problems parking your domain if you havent done the following:-
Changed your nameservers to point to ours as quoted in your setup email (Usually these are ns0.redbeck.net and ns2.redbeck.net respectively)
Registered your domain name
Edited the A record entry if not using our nameservers