Apple updated the Push Notification service, and as of November 2020, the Apple Push Notification service (APNs) no longer supports the legacy binary protocol. Apple recommends an update to the HTTP/2-based APNs provider API. When you use HTTP/2, you must also update the framework to use PKCS #8 because of constraints when PKCS #12 is used with HTTP/2: It is not possible to use a PKCS #12 client certificate for notifications on an HTTP/2 connection in .NET, and to deliver a Windows library that forces the usage of this certificate. Apple Push Notification service (APNs) requires to only use cipher methods that are available from Windows Server 2016.