Desktop macs have i message too, so a determined spammer could just make a bunch of mac vms. Getting a valid serial with an unconfirmed purchase date is a massive pain, though.

It worked for me as soon as I upgraded my Hackintosh to Catalina. I had an invalid serial number and board ID. Not sure why it suddenly worked.

Interesting, go figure. Maybe it's something about the upgrade process? I made a fresh one on catalina and had a mess of a time getting it to work.