To configure and enable push notifications for iOS apps, use the Apple Developer Portal to create and obtain mobile provisioning and push notifications (APNs) certificate files.
An Apple Push Notification service (APNs) certificate is required when using push notifications to send push messages from the server to an iOS mobile device. For more information about generating an APNs certificate, go to the iOS Developer Library.
Save the single private key and a single APNs certificate in a .p12 file so that it can be uploaded to the certificate set for the iOS custom app you are creating. For more information, see Configuring push notifications on iOS.