I had a similar problem. I was not getting sandbox server notifications when running through the simulator. But when I tried through TestFlight, everything worked.
This has a table that says that JWS receipts are not provided through XCode testing - https://developer.apple.com/documentation/storekit/original_api_for_in-app_purchase/testing_at_all_stages_of_development_with_xcode_and_sandbox
renarl
Users receive reputation points by contributing quality content to the forums.
Posts include post and replies published on the forums.
Post authors can mark replies as Accepted to indicate successful solutions.
Apple Developer Forums admins can mark replies as Apple Recommended to indicate an approved solution