Cpanel error - The certificate could not be installed on the domain. You must use an IP address that is on the server.

If you try to install a Let's Encrypt certificate you might encounter this error.I experienced this when I installed a multi-domain certificate and it installed properly for a domain and then CPanel refused to install it for other domains with this error. (I tried it on a Godaddy shared host.)

The solution according to some net forum  posts is just wait and try again later or the next day.

I tried installing the certificate again on the next day and then it installed without any problems for the other domains too.

So it seems it's an intermittent error only which goes away.