Catalina software update OK except for iMessage

I've just upgraded from Mohave to Catalina via software update. The process went smooth, almost like a regular Mac. One of the few things I've noticed so far is iMessage not working. It did work in Mohave. Otherwise I seem to be logged into iCloud OK.

What are some things I could look into to rectify? The error is "Could not sign into iMessage. An error occurred during activation. Try again."

Thanks,
Mark

submitted by /u/mdurg68
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