Secure site not available
Most likely, the web site simply does not support HTTPS.
However, it’s also possible that an attacker is involved. If you continue to the web site, you should not enter any sensitive info. If you continue, HTTPS-Only mode will be turned off temporarily for the site.
[Continue to HTTP site]
(Copied from Firefox on Android)Personally I think that's reason to do it alone, for the price of a free Let's Encrypt cert you can deliver much better UX. You presumably want people to visit your site.