Alright, time to put some closure to this 6rd issue.
I decided to revisit the problem again and found that everything was working, no more "Invalid IP" message.
The problem turns out to be that "Primary DNS Address" is a required parameter. OK, that's fine but it would be nice to have a more descriptive message indicating what piece is incorrect or missing. Most users out there will probably use their IPv4 DNS servers to resolve IPv6 AAAA DNS requests so I think leaving the field blank is a valid config.