Can't add separate domain to Google Apps account

Question

I'm trying to add a separate domain to my Google apps account (different from a 'domain alias'). However the button that used to appear on the 'Domains' page seems to have disappeared.

I've added two domains using that button in the past, but now it's gone. The official limit is close to 600 and I'm at 2 so far...

Screenshot:

Answer 1

So turns out Google just changed their policies and now

"The legacy free edition of Google Apps only supports domain aliases, not secondary domains."

I'm guessing this was to fight against all of the legacy accounts being sold on eBay.