Xamarin forms android Application not getting DeviceToken Parse SDK
when you have declare the push notification using xamarin then you have to write code on both section like xamarin android and IOS, and also if you have used to remote notification then use to push sharp lib which is a best for push notification and register your app and enable to notification service like GCM and APSN relevent to android and IOS.
Plese try this : https://github.com/rdelrosario/xamarin-plugins/tree/master/PushNotification/PushNotification