Unfortunately, to be able to use your custom domain with our hosting you’ll need to change the nameservers first, as forwarding with masking is most likely blocked by this system:
The process is documented in the article linked above by @solace-ken:
After changing your nameservers to ours, you can add your domain to your hosting account, either as a Parked Domain or an Addon Domain depending on what you wish to do (check out this article for more information):
Now, you may change the nameservers back to your registrar’s default ones. You’ll need to add DNS records there to make your domain point to this hosting; the most easy way to achieve this is copying the “Website IP” value from the account section of the Client Area’s and adding it as an A record on your domain):
