Unable to download Apple Developer keys after initial creation
You can't re-download the IOS Push Notification Auth key. Only public key is retained by Apple and a private key which you retain and protect.
See documentation section Provider-to-APNs Connection Trust.
Token-based provider connection trust: A provider using the HTTP/2-based API can use JSON web tokens (JWT) to provide validation credentials for connection with APNs. In this scheme, you provision a public key to be retained by Apple, and a private key which you retain and protect.
You can see warning too when you create an Auth Key.
Download and Back Up After downloading your key, it cannot be re-downloaded as the server copy is removed. If you are not prepared to download your key at this time, click Done and download it at a later time. Be sure to save a backup of your key in a secure place.
