Thanks for trying to help. In fact, it was the complexity of the whole process that confused me. Authentication was being done by DNS. As with many awkward IT problems, there were two issues. In addition to the expired certificate for the domain in question, the certificate for the server that automates the DNS changes had also expired. The message related to the request to update the TXT records. That certainly wasn't clear to me, and I guess it wasn't clear to people who kindly tried to help either!
2 Likes