Hi, variable replication only works one way. From the server to the clients, there is no client to client communication. So if the server changes a replicated variable, then it will be updated for all relevant clients. If a client changes a replicated variable, it will only be changed locally for that client, nobody else will know about this.
If you want the client to tell the server something, you need to use a RunOnServer RPC (create a custom event, make it RunOnServer, second from the top here (search for ue4 run on server Replicating Functions in Blueprints) the direct link to that documentation page seems to be broken). The Server will then execute that event. So in your case
