Hey there, i am sorry if you don’t understand english, because this is all japanese. Still i translated your text and see that you have problems with the sessions, steam and online playing. Maybe someone can translate my answer if the questioner doesn’t understand it.
OnlineSubsystem NULL limits you to LAN Games or Online games where you can only join over the IP. This is due to a missing Master Server. Without a Master Server, the Search Sessions Node (or C++ code) has nothing to ask for a Server List. This is where Steam and other Subsystems come in handy. Due to the AppID and Steams Master Server, you will be able to search and find online games. Although it could be that using the Test AppID 480 will not work.
Also Steam and other subsystems don’t work in the Editor. If you just press Play, you will always play with the NULL Subsystem.
You can start the game directly with “-game” in the command line of VS. You can also try to start it by going to the project directory and right clicking the .uproject file, selecting “Launch Game” or something like that.
If Steam is running and you set it up correctly, you will see the Steam Overlay popping up on the lower right side. If not, you may want to check the LOG Files and see what is going wrong.
@eXi
Yes thats basically what I wrote too :) The SteamOverlay now pops up in his 4.8 Packaged Project, but he can’t find the session over steam. So last thing I told him is to include URL Name, which I think is necessary.