Web unsecure connection

Currently, we have VPN locally hosted, both ports 80 and 443 are port forwarded.
One of our concerns is that when using the WAN IP to access the web page it shows the login page with unsecure access via https. How can we limit this to redirect to our actual subdomain name instead of showing this page when someone tries to access it?

A valid certificate needs to be configured to allow HTTPS access without the certificate error. The Lets Encrypt support can be used to configure this.

I meant accessing it via WAN IP instead of the domain name, my SSL certificate is working.
For example if I try to access the server via https://000.000.000.000 it is still visible and not redirected or unavailable.

You would need to configure an external web server that could handle that redirection. Blocking web access from the IP address without a domain correctly configured could break the Pritunl Client. Unless the sync address is set in the Pritunl host settings it will fallback to the host public address. If these are both IP addresses the Pritunl Client will not be able to sync the configuration. Dynamic firewall and WireGuard connections are also done using the sync address.