Question
When logging in to Plesk using server's IP address (e.g. https://203.0.113.2:8443 or https://203.0.113.2), an SSL warning appears in a web-browser.
Is it possible to secure a Plesk IP address with an SSL certificate (Let's Encrypt / other certificate authorities)?
Answer
Plesk IP address cannot be secured with a Let's Encrypt certificate, as Let's Encrypt does not support securing IP addresses. For more information, visit this Let's Encrypt thread.
In order to secure a Plesk IP address, it is required to purchase a certificate from Certificate Authorities that provide such an option. An example of such certificate is OrganizationSSL certificate by GlobalSign, which allows securing public IP addresses. The paid certificate can then be installed as per the KB article: