Client fails to Join Session?

I’ve been following the tutorial series on YouTube “Blueprint Multiplayer v4.11” and can’t figure out why the Client isn’t joining the session?

(4.27) I haven’t implimented Steam Online Subsystem I think everything is out of the box. I run as Listen Server with 2 number of players. …

If I use on the Client “open 127.0.0.1” it seems to work.