Where is documentation for writing the local push provider server

Developers must define and implement their own data protocol and transport mechanism (i.e. a TLS socket connection, preferably using the Network framework) back to their server that is used within the NEAppPushProvider.

The SimplePush sample code project contains a basic example server for demo purposes (SimplePushServer) who’s data protocol consists of JSON encoded messages. However, we expect that most developers will implement their own backend push services platform or integrate their apps with existing VoIP and text messaging solutions.

Where can we find the the “SimplePush sample code project”? It does seem to be showing up in the searches or the download sites.

https://developer.apple.com/documentation/networkextension/local_push_connectivity/receiving_voice_and_text_communications_on_a_local_network