Just noticed the same thing: LetsEncrypt SSL certificate generation generates an error message saying it failed, even though the generated certificates are in fact valid, in the current Virtualmin 8.1.0 GPL
After an automatic or failed SSL generation, the following message comes:
.. request failed : Web-based validation failed : Expected full certificate file /etc/letsencrypt/live/mysite.ch/fullchain.pemKeyissavedat:/etc/letsencrypt/live/mysite.ch/privkey.pem was not found
Interestingly, if one looks at the generated certificates in /etc/letsencrypt/archive/mysite.ch and manually pasts them in via “Update Certificate and Key”, the certificates do work.
Enclosed is the corresponding letsencrypt log.
letsencrypt.log.zip (20.7 KB)