Port forwarding not working with IP Passthrough/Double Nat

Hello,

Recently I've been trying to portforward a game server through my BGW210-700 gateway, but the port hasn't been able to be opened. It's currently connected to my router and that router is connected to my PC.

I'm a little confused on how IP-Passthrough is supposed to work, but I've gone through the steps of setting it up on the gateway's settings and restarting it.

I've tried double-natting without IP-Passthrough, but the port still doesn't open.

If I could get some help with setting this all up, that'd be great.

Thanks