Hi there, (sorry expose, had already put this together ) so here we go, this is all you need:
The PlayerController runs on the owning client and on the server. So this is the place to put your replicated Event.
So you just need to create the MessageReceived EventDispatcher.
Your Widget with the TextBox: The widget just needs to listen for the Shout-out from the PlayerController when a Message arrives, so here we go:
happy to help, Marooney