Google DDNS support?

I see in my ac87u's ddns page that google-ddns is an option. I recently bought a google domain name so figured it would be nice to be able to forward a sub domain. So I set it up with all the info that works via the ddns web update and various clients but every time I try I get an error popup of:
Unauthorized regristration request

So has anyone successfully used the google ddns option or know what I might be doing wrong?