UE4 Blueprint Multiplayer, can't join session

Hey all.

So I’ll cut the chase. I’m having issues with this tutorial series regarding joining a session. My testing conditions are as follows; two different PC’s, two different Steam accounts, connected to the same internet, running the game in stand alone. I have one PC host the session and the other try to join (duh). The only problem seems to lie with joining the session. The search finds the session to join, but when I hit the accept button to join it, it pops up with the error dialogue and a forever running loading screen in the background.

I have gone back several times, checking the blueprints against the tutorial to no avail; my blueprints are correct as far as I can see, so I’m not sure what the issue is.

Below is a gif of what happens when I try to join a session:
http://gph.is/2nI9YIc

Below are screenshots of (I think) the relevant code:

So yeah, I’m very stuck with this. If you need anything else (more screenshots, a more thorough gif/video, defaultengine.ini lines), just let me know and I’ll upload it as soon as I can. Thanks in advance.