The first step is to check your web site has HTTPS enabled. To do this, simply go to the front page of your site and then edit the address in the browser so it uses HTTPS instead of HTTP. For example,

https://www.demo.xyz/

If you see an error in your browser that the site is untrusted, or that the connection was interrupted, or any other browser error, then SSL is NOT running properly on your site. You should contact the host or your developer if you believe it should be.

Only once you have verified that HTTPS support is setup and working should you attempt to activate the SSL/TLS support within Kartris.