Cross-Platform / Cross-Engine is great. Inside the web client I can hear the UE client, but I cannot hear web clients inside the UE client. Why does it not work?

Usually, every player character inside UE is spawned as soon as replicated by the network engine, i.e. Unreal networking. When an ODIN peer joins that cannot be replicated, you should either spawn a placeholder object “On Peer Joined” or you can attach the synth component of non-UE clients somewhere else “On Media Added”. For instance, you could attach it to your local player character to hear web clients with 2D audio like they are “on the phone”. Or you can put a virtual radio box inside the level to let web clients speak through that object. It is also possible to create a second ODIN room (e.g. “global chat”) and inside let all players from all client types communicate in 2D - in addition to the in-game (UE-only) spatial audio voice.

Remember to detach / destroy objects from non-UE ODIN peers when they leave the room.