public void PlayFabMultiplayerManager.Get().SendChatMessage(string message, IEnumerable<PlayFabPlayer> recipients, DeliveryOption TBD);

PlayFabMultiplayerManager playFabMultiplayerManager = PlayFabMultiplayerManager.Get();
PlayFabMultiplayerManager.Get().SendChatMessage("Hello", targetPlayers, DeliveryOption.Guaranteed);