I ran into this error when trying to have a certificate issued for what I assume is a relatively high-value domain. Would it be possible to request to have this domain whitelisted? I’d prefer not to state the name of the domain here in a public forum (although I will if that’s the only way to communicate with the Let’s Encrypt team). We have a partnership with the entity in question, and they have already setup a CAA record to allow letsencrypt.org to issue certificates for the specific domain we are setting up with them.
Happy to provide any other information that would be helpful here. If the answer is no, it would be great to know as soon as possible so we can try something else.