Invalid License Unknown

One of my sites have problems in both

Both responded with similar message
{"code":"unauthorized","message":"Invalid Licence 'Unknown'"}

Other sites are not affected.

I have restarted both the control panel server and the apps/database server, but the problem persists.

Please advise on how to fix.

Thanks
Jim

Can you try to re-save your Enhance license from settings ? also check there is no open-invoices in your account at : my.enhance.com

Re-saved license and no outstanding invoices.

Same problem.

The most common cause of licence issues is:

System time is incorrect. The time forms part of the licence handshake and needs to be correct within a few minutes.
Lack of connectivity. Your server needs to reach out to our licence server. If outbound DNS is broken, Enhance can't contact the licence server to validate the licence key.