Have a clue what is behind The HTTPS URL:
* SSL Server Test (Powered by Qualys SSL Labs)
https://www.ssllabs.com/ssltest/
* SSL Checker - SSL Certificate Verify - SSL Shopper
https://www.sslshopper.com/ssl-checker.html
* SSL Certificate Checker - Diagnostic Tool | DigiCert.com
https://www.digicert.com/help/