Unable to join game session

[Lander07]

Hi, I have a problem with multiplayer games.
When I want to play with a friend, I get an error: Unable to join game session, and I don't know how to solve it.

[Dss0]

Lander07 the host may have to forward port 3074 udp (https://www.lifewire.com/how-to-port-forward-4163829)