Hi ,
thanks for your reply, that helped! I’ve managed to get my full friends list from steam and display the information like friend’s name, online status etc. in a printstring on screen.
But I’m struggling with the invitation itself. Every time I grab a UniqueID with index X from the friend’s array, I can display the friend’s information properly but the invitation fails. As a simple test I tried to invite myself as you can see in the attached screenshots. This works fine except that I don’t get a steam overlay that notifies me about the invitiation (The overlay in the attached screenshot is the basic “Steam is active” overlay that show up when you start a steam game)
And I’m wondering why I need to plugin a player controller into the node and not only the Unique ID if you want to send an invite to a friend from your steam friend’s list who is currently not in your game and who doesn’t have a player controller at this point?
The whole subsystem is still quite confusing to me and I would be really grateful if you could clarify the procedure of inviting steam friends to your game 
Thanks and best regards,
Daniel