Upon initial access to Plesk control panel via HTTPS (eg. https://1.1.1.1:8443), your web browser will show-up with a warning message saying that it can't verify the SSL cert.
The message may vary, depending on the browser. For instance in Firefox it will say "This Connection is Untrusted".
It can be safely disregarded, the browser is showing up with that warning as it's not able to recognize self-signed cert (web browser can only recognize those SSL cert that you purchase from CA like Verisign, Geotrust and etc.). Click on "I understand the Risks" > "Add Exception" > "Confirm Security Exception".
After that, you should be able to see the login page of Plesk control panel.
