"Contact key verification is temporarily unavailable for your account."

Set up Contact Key Verification on my iPhone, and then checked it my iPad and Mac. iPad looked okay. Mac says "Contact key verification is temporarily unavailable for your account."

Turned it off and turned it back on. Same issue.

Followed all of the steps in this article below under the heading "If you get an alert that there's an issue with iMessage Contact Key Verification." None fixed the Mac.

If you get an alert from iMessage Contact Key Verification - Apple Support

Current status: Contact key verification is OFF on iPhone and iPad. But it's stuck in the ON position on the Mac. When I try to turn it off, it hangs for a while, then tells me Contact Key Verification not available and to check the internet connection, which is fine.

I have tried hitting the Reset Contact Key Verification option on appleid.apple.com, but that doesn't seem to do anything. The setting stays switched on on my phone, and the public verification code is identical.

Has anybody fixed a similar issue?