Multiplayer ActorOnClicked get player who clicked

So basically I want to be able to click NPCs and Monsters with a left/right click to interact with them.
I need to know what I clicked (if I can put the onClick event into the NPC/Monster I have a reference) and I
need to know who clicked it (I have no idea how to do that). I tested the ActorOnClicked event and it works fine
if I am the server, but it doesn’t work when a client clicks it. It always returns the same Client id (-2).

I found this solution but to be honest I barely understood anything. I am kinda new to ue4 and used
to only program in C# for a few years now. It looks like I need to handle every NPC/Monster in the PlayerController
class and need to find the object I click on by the position my mouse is on. Is that correct?
How do I get a reference to the object, that lies under my mouse cursor? And isn’t this a very inefficient way to
determine my target?