iMessage and Facetime "error during activation"

I get an "error during activation" when I try to sign onto to iMessage and Facetime on my iMac running Mojave. I've tried turning off Apple's Firewall, Sophos anti-virus, and my VPN. It still doesn't work. I can sign onto my Apple ID fine, and so it is not my password or account. I've looked around for other suggestions but found none that worked. Should I somehow delete both iMessages and Facetime and re-install? Or delete any library preferences that I find with "imessage" or "facetime" in the file name?