Cannot join sessions through LAN

Hi. I want to build a multiplayer game. I have watched some videos about sessions. But after creating a session in server side (hosting), my client side cannot join the sessions.

(The post was asking for finding sessions until I found my careless mistake.)

I have added two lines on the DefaultEngine according to videos.

Here is the controller.

And the instance.

The menu should be okay. I upload it also.

Create session is done successfully with moving to the level. But join session is failed with printing string “Join session error”.

I find a similar question and it seems no solution…

Will there be some problems from my notebook or router?