If iMessage contact key verification isn’t working

Hi there,

Please try this

• If you can’t resolve an issue with Contact Key Verification, you might be able to reset it:
  • If you no longer have access to a device with iMessage Contact Key Verification turned on, you can reset it from the web: At account.apple.com, select Sign-In & Security, choose Contact Key Verification, then select Reset Contact Key Verification.
  • If your device is running older software, you might also have the option to reset in Settings: Go to Settings (or System Settings) > your name > Sign in & Security, then look for the option to Reset Contact Key Verification.

See this link for further reference

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

This might help: If you get an alert from iMessage Contact Key Verification - Apple Support