As I expected this is a replication issue. You are spawning client side and then trying to move the projectile server side. As only the server has authority to replicate the projectile is not known by the server.
You need to spawn the actor on the server. Also Do note that you can only call the server with rpc if you own the actor calling it (aka if it’s from pawn controlled by the client)
Try to call the whole block from a custom server side rpc and see what it does I can’t see your whole code but the approach doesn’t seem right at all. I would help more but I’m currently on my phone 