Actually it works.
If i remember, it is this line:.inFocusDisplaying(OneSignal.OSInFocusDisplayOption.None) that prevents a pop up message for the notification when game is in foreground.
There is already a handler there, for this case where you can pass a keyvalue on blueprint node. So you can show your own message with umg.
It is very basic implementation and everyone could do his own thing, that’s why i didn’t mention it in the post about onesignal.
With few tweaks in java cpp, you can have a messenger application’s functionality, with few umg and blueprint nodes for your game.
I just gave the instructions to send notifications to your games.