Multicast works only on one client

I create Mulcitacast event, which prints Hello, and connect it to action press I, but after pressing message sends only on client, where i pressed button, not on all. How can i Fix?

Multicast should be called from the server. If you call it from a client then only that client will receive a call.
The way to do it is to create another Custom event and set it to run only on server. Now get that event to call your Multicast event. Change your button so it only calls the event that is set to run on server only.

  ButtonPress -> EventOne(run on server)
   EventTwo -> Print Stuff