What is the best way to trigger App Store Server Notifications to test your endpoint? There is a document on Request Test Notification but this only has information on the URL without any info on the expected request parameters, etc.
The ideal experience would be that StoreKit2 debugging inside XCode fires server notifications to a specified URL, but it doesn't seem to be supported.
It's not immediately obvious, the but those URLs need to be signed. This is a fairly complex process. There's a beta (at time of writing) library called app-store-server-library that's in different languages like Python, Swift, etc. Check out the WWDC23 session on Meet The App Store Server Library, where they cover it in depth. You'll need to create keys and certificates, etc, to get the library working (and would have to do the same plus manual signing if you were to use something like curl to make the requests).
