Example of Push Notifications with OneSignal in Xamarin.Forms applications - http://julianocustodio.com/onesignal-push-notification

pushNotification.json

{
  
 "app_id": "ID DO ONESIGNAL",
 "included_segments": ["All"],
 "data": {"foo": "bar"},
 "subtitle": {"en": "Titulo para ios 10 ou superior"},
 "headings": {"en": "Titulo"},
 "contents": {"en": "Mensagem"}
  
}