here the basic data of our problem:
My domain is:
I ran this command:
Certificate request in Plesk App “Let´s encrypt”.
It produced this output:
Invalid response from https://acme-v01.api.letsencrypt.org/acme/authz/ZJ-zwYzdOE0BGYXxT3iCvIw4yrrarzeFDDHk-njrkds.
Detail: The key authorization file from the server did not match this challenge [afpoJNZxCEnDao851hbCUhTRqlUZs1Ud50jxjzZJ7Eo.dy79C5ntjeiyKDOUk-clnTUStTXmWmCA7haFNVjDcpo] != 
My web server is (include version):
Apache 2.4.18 / nginx 1.11.10
The operating system my web server runs on is (include version):
Ubuntu 16.04.4 LTS
My hosting provider, if applicable, is:
I can login to a root shell on my machine (yes or no, or I don’t know):
I’m using a control panel to manage my site (no, or provide the name and version of the control panel):
We have virtual hosting on this server and have already created Let´s encrypt Certificates for some other domains. But if we try to create a certificate for this domain (pure domain incl. “www”) this error appears. The key file is created in folder “/.well-known/acme…” and can be called from outside.
For the same domain we already created a certificate for subdomain “cloud” some months ago.
Because of this, now we made separate DNS A-records for “cloud” and “www”, because someone told us, this possibly could help. But it did not.
Do you have an idea what the solution may be?
Thanks for your help in advance!