On failure always with Find Sessions node


I try to create a mini game for learn the multiplayer system, but I’ve a problem with the find Session Node.
With 2 players, i create the game with the first, it’s ok, but when i try to click on the join button, it return me the print string value (failure) all time.

For this, i’ve follow this tutoriel, in french Unreal Engine 4 LIVE [MrFeuilleVerte] | Création d'un jeu de tir en multijoueur - YouTube

I try to reinstall unreal, use another version, in LAN but same problem

Sorry for my english, i’m French