There had been a problem with that specific domain, and LetsEncrypt (from where the certificates are registered) was complaining that we couldn't get a new certificate as we already had too many. (there's a limit of getting five per week per domain)
I'm not exactly sure why it had rate limited that domain but none of the others on our system. I suspect a temporary problem with the domain had resulted in too many retries to get a certificate.
Anyway - I've been able to manually get a certificate for that domain and install it on the server - and from here on it it *should* be fine, and it should renew automatically when necessary.
Cheers
Joe
Perfect, thank you very much! It is all working correctly now.
Perhaps it is our fault as we changed the settings for the domain a few times, so perhaps it was triggering the e-voice system to renegerate the certificate and we hit the limit?
Anyway, it is all correct now.
Thanks again for the rapid and helpful response.
Kind regards, -Paul