You cannot get certificate from Let’s Encrypt for IP. Only for domains.
That is correct, but that isn’t what @Joshua_J tried to do (even if it is, somewhat confusingly, what he suggested in the topic heading). Rather, he tried to issue a cert for 'nextcloud. That’s also invalid, of course, for two reasons:
- The ’ character isn’t valid in a FQDN, and
- There’s no domain name present, only (at most) a hostname.
@Joshua_J, in order to get a cert from Let’s Encrypt, you need to own or control a real internet domain–either buy one from your registrar of choice (I like name.com lately, but there are plenty to choose from), or get a free one from freenom.com and deal with their mildly-annoying renewal requirements. You’ll then need DNS records pointing that domain name to your installation.