silentPush property
Specifies whether the notification is a silent push notification. A silent (or background) push notification isn't displayed on recipients' devices. You can use silent push notifications to make small updates to your app, or to display messages in an in-app message center.
Amazon Pinpoint uses this property to determine the correct value for the apns-push-type request header when it sends the notification message to APNs. If you specify a value of true for this property, Amazon Pinpoint sets the value for the apns-push-type header field to background.
Apple has indicated that they will throttle "excessive" background notifications based on current traffic volumes. To prevent your notifications being throttled, Apple recommends that you send no more than 3 silent push notifications to each recipient per hour.
Implementation
final bool? silentPush;