Unable to access Plesk with the following error shown in a browser:
In Mozilla Firefox:
CONFIG_TEXT: The owner of server.example.com has configured their website improperly. To protect your information from being stolen, Firefox has not connected to this website.
This site uses HTTP Strict Transport Security (HSTS) to specify that Firefox may only connect to it securely. As a result, it is not possible to add an exception for this certificate.
server.example.com uses an invalid security certificate. The certificate expired on September 06 2017 The current time is October 05 2017 Error code: SEC_ERROR_EXPIRED_CERTIFICATE
In Google Chrome:
CONFIG_TEXT: Your connection is not private
Attackers might be trying to steal your information from server.example.com (for example, passwords, messages, or credit cards). Learn more
Browser console detects that the SSL used for securing Plesk page server.example.com is valid for *.example.com domain and expired in the past.
Expired SSL certificate is chosen for securing Plesk in Tools and Settings > SSL/TLS Certificates > Certificate for securing Plesk.
Log into Plesk using the server IP address instead of the hostname, for example https://203.0.113.2:8443.
Check which SSL certificate is used for securing domain
example.com: Domains > example.com > Hosting Settings.
Secure Plesk with an SSL certificate using the instructions from the article How to secure a Plesk hostname on port 8443 with an SSL certificate (Let's Encrypt / other certificate authorities).