The site's security certificate is not trusted!

[misak35]

You attempted to reach some.domain, but the server presented a certificate issued by an entity that is not trusted by your computer's operating system. This may mean that the server has generated its own security credentials, which Chrome cannot rely on for identity information, or an attacker may be trying to intercept your communications.
You should not proceed, especially if you have never seen this warning before for this site.

This is vesta panel site url https://domain:8083
How to fix this.

[skid]

That's right, the default certificate is self-signed which means that your users have to make a decision whether or not to trust it when they access control panel.

If you have an signed SSL you can easily install it. Just replace the content of the following files and restart vesta service
/usr/local/vesta/ssl/certificate.crt
/usr/local/vesta/ssl/certificate.key