We recently added support for custom domains to YDNS. That feature allows you to have YDNS manage your DNS records for your own domains. That makes YDNS not only offering free dynamic DNS services but also DNS services in total, since we added support for a few more record types as well.
I see many people adding domains the wrong way. Our system currently does not test whether a domain exists or not; it will frequently check its nameserver records for correctness. If they are not configured correctly, YDNS will disable those domains for further use (this will also happen if you have successfully validated your domains in the first place, but changed its configuration afterwards).
To correctly add your domain to YDNS, follow these steps:
Login to your Domain registrar’s Control Panel. It shall offer a section where you can change the nameservers which are responsible for your domain. If you cannot find this, you cannot add your domain to YDNS. In case you successfully found the appropriate section, replace your domain’s name servers with these two (and of course delete the previous one if they still exist after that):