I requested a linux expert to check and he said this,
"I've installed the certificate and setup the litespeed vhost/listener for it. Works fine in some browsers but says it's insecure in chrome (but it is secure). This looks like a bug between litespeed and directadmin virtualhosts. It's best for you to contact litespeed in regards to this, as it looks like an incompatibility bug."
Please guide me what to do to correctly install SSL.
The certificate itself is loaded fine, when access the https:// website, it return error code 500, and include some none-secure content, that causes warning from browsers.
It is a site configuration issue, need to make it HTTPS friendly.