Follow these steps:
1. Generate an APNs Auth Key
Open the APNs Auth Key page in your Developer Center and click the + button to create a new APNs Auth Key.
In the next page, select Apple Push Notification Authentication Key (Sandbox & Production) and click Continue at the bottom of the page.
Apple will then generate a .p8
key file containing your APNs Auth Key.
Download the .p8
key file to your computer and save it for later. Also, be sure to write down the Key ID somewhere, as you'll need it later when connecting to APNs.
2. Send Push Notifications
Ref: APNS (Configure push notifications)
Important: Save a back up of your key in a secure place. It will not be presented again and cannot be retrieved later.