I installed OpenProject 8 on a dedicated Ubuntu 18 VM in our office. I then connected this VM to our VPN server so that it can be accessed from the outside world using a domain name. On the VPN server, I set up a VirtualHost with an SSL certificate and a reverse proxy pointing to the VM. The same SSL certificate was copied to the VM.

Expected behavior (works with NextCloud with a similar setup): OpenProject can be accessed by anyone, anywhere, through the domain name.

Actual behavior: Attempting to access OpenProject through the domain name redirects to the VM's IP address, which therefore only works if the client is itself connected to the VPN server.

Attempted solutions that don't work: Using ProxyPreserveHost on the VPN server, directing the VPN server's VirtualHost directly to the OpenProject port on the VM (bypassing the VM's own VirtualHost), attempting to set up OpenProject without SSL on the VM.