Routing ports to certain computers

[mw92706]

I have a server which I'll call "Echo" connected to a GL INet GL-MT300N router ( https://www.gl-inet.com/products/gl-mt300n/ ) which is connected as a client to my OpenVPN server. Echo needs direct access to certain ports for two way communication. For example's sake, let's just say the port is 5198.

ECHO's public IP address is the address of the OpenVPN server. I'll just make up an address and call it 104.105.106.107.

So to the outside world, when ECHO makes an outbound request on port 5198 they see the IP address 104.105.106.107 on port 5198.

When other computers outside the VPN make inbound request to Echo, they're going to use the public IP address 104.105.106.107 on port 5198.

I have already opened up ports on the router to make sure inbound and outbound traffic routes directly to Echo's internal IP address which is 192.168.8.182 - a static assignment from the router.

I have also opened ports at the OS level on the OpenVPN server itself. So there shouldn't be anything blocking port 5198.

Within the OpenVPN settings is where I'm lost. I have the community edition. Surely this must have been discussed before so if there's a previous post I didn't find, feel free to link to it. Aside from that, does anyone have a clue as to how I can get that client to be accessible to the outside world through port 5198?