Send message on websocket

We have used Akka to develop our chat engine. We are using Play 2.4 and Legacy websocket implementation with Actor. This is working fine without problem.

I want to migrate to Play 2.7. this has integration with WebSocket and Actor using Flow. I am able to send message from client and receive it on server.

But I am NOT able to push message from server to client. Can somebody help me know how to achieve this in Actor using Java?

Previously we had access to OutputStream so was difficult write to it. But now i dont see that option.