Its custom variable for easier setup.
Well the server can’t even attack the client that’s what i mean
Your event is not RPC event. Apparently you don’t know unreal blueprint replication basis, you should watch some guides.
No that’s why i said that the server can’t attack the client , it can’t even attack a character controlled by no one (if i drag and drop the character into viewport)
OK i fixed the problem.The problem originally wasn’t with my replication but the attack itself not replication to the server !Still thanks for the help mate keep it up 
A few days ago I had the same thing “Client can’t apply damage to server”. Lost about 12 hours on it.
So the reason was that I didn’t mark “Replicates” checkbox in my Weapon-actor.
So mby you need checkout all these things with replication again
Yeah I managed to fix the problem mate but still thanks for the help ! Good luck on your project