Use the project template provided:
Download Advanced Session plugin: Place in Plugin folder in the Unreal project location
Open UE → go to WBP main menu page:
Open the BP of WBP, click ButtonCreateSession, then click On Clicked Green View button to open Eventgraph
Tick Use Lobbies Voice Chat if available, and Use Lobbies if Available
Go down to Find Sesson Advanced node, change to Client Service Only, and tick Search Lobby:
Complied