GL-MT300N-V2 Port Forwarding

Hi, looking for some help.
I have an Asus RT-AC68U router configure with dynamic dns.
I have a GL-MT300N-V2 connected to it and running a VPN client on it.

So I have

Internet --Asus RT-AC68U–GL-MT300N-V2–Devices

The devices connected to the MT300N-V2 can get out to the internet and are effectively running through the VPN connection.

I’m trying to go the other way. Get to the devices from the internet.
I have setup port forwarding on the ASUS to forward for example port 215 to the GL-MT300N-V2
I’ve also forwarded port 215 on the GL-MT300N-V2 to the static IP address of the device.

If I use Open Port Check Tool - Test Port Forwarding on Your Router it just shows port 215 closed.

The port forward rule I have on the mini router is
IPv4-tcp, udp
From any host in wan
Via any router IP at port 215
IP, port 215 in VPN_client

So I am stuck as to how I can’t get through from external to the device.
Any ideas ?

Can you just port forward port 215 to MT300N-V2 and then open a port on MT300N-V2 to see if it works?

Because you have double port forward you need to verify one by one.

I tried putting the MT300N-V2 in the DMZ of the Asus router which in theory should expose it directly externally.
But I still don’t seem to get it to work.
Is there something I need to do on the MT300N-V2 that allows it to forward from the WAN side of the router through to a device that is running on the VPN client ?

Does this look right ?

Sorry for multiple replies, just trying to add more info.
I did some more testing. I can open ports on my Asus and verify that it can get through externally to those ports.

So I know I can get the traffic in and pointed at the MT300N, I just can’t seem to get it to forward on to the device that is connected as a VPN client on the other side.

I have Public IP – which traffic comes in and gets forwarded to the port on the router @ (Static IP assigned to the MT300N). I’m then forwarding on the MT300N to a device connected to it which is

Is it because that device is running via the VPN client which when connected is on yet another IP address that is the issue ?

yes vpn is a problem.
When you turn on vpn client on MT300N-V2, you can port forward from your Asus to it.

But you cannot port forward to its client easily because of vpn firewall. Actually you can do this be setting up in luci. But there is a lot of interfaces so I am afraid this will break the vpn anyway.

I have

internet box
the VPN server (GL-MT300N-V2)
Client VPN (GL-AR750S)
device lan

if I put the device lan on the MT300N-V2 and open the ports, I have good access
but I can’t do it anymore when the device lan is on the AR750S

I opened the ports under IP/index#/firewall firmware 3.022

How can I access the device?