Hello,
Thank you for the information.
If you want to use port-forwarding with OpenVPN, then the port-forwarding rules should have OpenVPN zone as the source zone and LAN should be the internal zone, and the internal IP address will be the address of your LAN device that you are trying to reach. You will need to specifiy the protocols and port numbers that you want to port-forward.
However, I would suggest configuring the server with a route to the TRBs LAN network. If you are using OpenVPN with TLS, you can take a look at the forum posts here and here. Keep in mind that, if the server has multiple OpenVPN clients and you want to add routes to them, the LAN networks on your clients should not overlap.
Kind Regards,