Trying to use any .gg domain triggers the “Invalid domain name provided” error.
I’ve added .gg domains to the billing portal.
For anyone reading this that faces a similar issue in the future: Our ordering software, WHMCS, does not have an up to date list of TLDs. This is not the same software that we use for mail hosting, only for order provisioning. Considering that you can rename and add domains in DirectAdmin after ordering, don’t feel obligated to register with the correct initial domain if you don’t want to wait for us to add the TLD to the order form on request.