To be clear, is it a http connection or https?
Unsecure could also mean its a mixed content warning.
Either you setup virtualmin to redirect http to https by default or you use .htaccess as an example.
If you use .htaccess already, then please show us the content of it (related to the redirection).
Edit:
The following code should actually do the trick:
RewriteEngine on
RewriteCond %{HTTPS} !=on
RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]