So according to you screenshot,
it should be “run on server”, and not “run on owning clients”.
The reason behind this is possessing can be only call from the server (autorithy) to avoid cheating (imagine if you can posses the player of someone else).
Here, you execute on Owning client, that mean you want to run the function on the owning client but :
a) Like multicast, this is only allowed to be run from the server
b) There is no owner on the moment, and when there is no owner, the owner is the server (by default).
Don’t panic, i’m french too, and you’re english is probably better than mine 