Hi there, true, no one wants this to happen. That is why clients are not even allowed to send data to other clients 
Only the server can replicate variables or multicast events to all clients.
There is only one way for the client to communicate to the server:
Create an Event where you set Replication to “Run on Server”. If you call this within your blueprint, only the server executes the event. (In the background it gets sent over network or just executes if it is already the server.)
So now you need a Blueprint that both Client and Server have. PlayerController fits the best in most cases.
Hope that helps Marooney