Use of UPnP / Gluetun port forwarding implementation

[luaxlab]

Hello folks,
I have a VPN provider that allows UPnP (hide.me).
The UPnP server lies at 10.255.255.250:1900 and when using upnpc from my local machine, I can actually open a remote port that is publicly connectable!
Using docker exec -it vpn sh, if I run upnpc in the vpn container, it times out saying that no server is to be found.
If I lift all the firewall rules and allow all connections and run upnpc -l the server 10.255.255.250:1900 will actually be found, but it can't be connected to (timeout).
Im trying to figure out how to allow this UPnP transaction to be run succesfully, and how that relates to
https://github.com/qdm12/gluetun-wiki/blob/main/setup/options/port-forwarding.md, which sadly lacks documentation.

Do I need to add any ports in the compose? To my knowledge, that would open them to my LAN, which is not what I want.

I'd be thankfull for some advice there.

Cheers!