I believe it’s true that a properly set up session is required to make voice chat work in an internet multiplayer application. I had a programmer help me on this and even though I don’t fully understand the details I think in the end he implemented an online subsystem that takes care of proper session setup and matchmaking so that voice chat works. Apologies, I don’t understand enough to be more specific.
As far as LAN or Internet is concerned: that was my problem from the get go: in LAN my own setup worked (as detailed in my original post and my feedback below “Got it working…”) but not when running the app over the internet. For that to work I needed to have that custom online subsystem implemented. I went for that custom solution because I also wanted to avoid existing third party platforms like steam. This is all very experimental I guess and I would not suggest this is the best way to go. I myself have not yet taken this any further than to create a working demo.