Can't install SSL certificate on IP address or Localhost.
If you see the following error - Due to technical limitations, it's currently not possible to install an SSL certificate on an IP address or localhost. Please install the plugin on a publicly facing, worldwide unique domain name such as sslzen.com and try again.
It's because you are trying to install an SSL certificate on an IP address such as 18.104.22.168
Technically that's not possible because SSL certificate can only be issued to a domain name such as sslzen.com or google.com
The same goes for localhost, if you are trying to develop your website locally, Let's Encrypt (The certificate authority), won't be able to issue you an SSL certificate.
If you are installing the SSL certificate on a public-facing domain but still see the above error message, please contact us via the Contact Form in the plugin.