OnlineSession - session Key


I’m currently working on sessions, and i’m looking at the OnlineSessionSettings.h.
I don’t wanna enter in the details about why i need it here, but, i need to set the SETTING_SESSIONKEY.

The problem is that i don’t know what it is exactly and what value i should set in it.
According to the code, i think it’s an IP adress, but which adress ? Where can i find it ? Isn’t it an ip adresse but something else ?

I don’t find any documentation and no one talking about it. I just have the commentary in the code :
/** Setting describing the session key (value is FString) */

Thanks for your help.