Check whether turn.fieapa.com is reachable from the network you are on, and whether two devices on different networks can actually establish a media path through it.
Credentials expire. Generate a fresh pair on the server with
sudo turn-credentials icetest 3600 and paste them here on each device.
Run this on each network by itself. It asks the browser to collect ICE candidates and reports what came back — which tells you whether STUN and TURN are reachable from here.
Open this page on both devices, each on its own network. One starts a room, the other joins with the same code. Offer and answer are exchanged through this server — nothing to copy between devices.