I can't run a custom event "Run On Server" from client


I am really sorry to ask a basic question because I’m really new in the UE4 game, but I don’t find any answer which seems to fix my problem.

I’m making a simple fps in multiplayer. What I want to do is to spawn the player characters of the remotes.
So I had the idea I could do that by sending a “Client Ready” event when the client is ready to the server to let it spawn the player and so, send an other event to the client to let it possess the crated and replicated Player.

But I can’t make the “Client Ready” work on the server part. This is what I did :

May be I’m wrong on the manner I want to spawn this remote players, I don’t know.
I red on a thread than it is impossible to send a “Run On Server” NPC if the object sending it isn’t owned by the remote. But I tried spawning it in the level blueprint which I thought was red on the clients too (Am I wrong too ?)

Thank you !