Hi. I wish I could help. It looks like online multiplayer is disabled by default. Sounds like we have to modify engine code to get it to work which is beyond me.
By default, Lyra uses the Null subsystem, which only supports multiplayer in the editor or on local area networks
Quote from here.
https://docs.unrealengine.com/5.0/en-US/common-user-plugin-in-unreal-engine-for-lyra-sample-game/