- SSL certificate was installed on a website at Plesk > Domains > example.com > Hosting Settings;
- https://example.com is browsed fine;
- https://www.example.com produces an SSL warning in browser.
www. subdomain was not added to SSL certificate as subject alternative name by issuer.
Contact SSL certificate issuer in order to add www.* subdomain as subject alternative name (SAN) to existing SSL certificate.