[SOLVED] Can't send iMessages

[EverythingIsRed]

I followed the guide here:
https://www.tonymacx86.com/threads/how-to-fix-imessage.110471/

iMessage and FaceTime activated successfully. But I can't send any messages. It always says "<person> is not registered with iMessage".
FaceTime doesn't work either. It only says "Call using iPhone" which would use the iPhone SIM instead of actual FaceTime.

 

[EverythingIsRed]

UPDATE: Problem resolved.

SOLUTION:
Create a new administrator account. Sign in with your apple ID. iMessage and FaceTime should work on that account. Sign out and sign back in to your previous account. It'll be a little glitchy at first, but it'll work.