Lets Encrypt Issue

I just installed No-Ip as well as Let’s Encrypt. Both went without a hitch and had been, or so I thought, applied to my NextCloud server to enable HTTPS encryption. I logged off NextCloud, logged back in, and now I’m getting the invalid cert warning:

This site is not secure

This might mean that someone’s trying to fool you or steal any info you send to the server. You should close this site immediately.

Go to your Start page

The hostname in the website’s security certificate differs from the website you are trying to visit.
Go on to the webpage (Not recommended)