I have 2 iOS app products. One can fetch subscription product information normally, while the other fails with the error errorCode 4040004 'App not found' in Sandbox. The App Store Connect backend configuration should be fine, and the subscription code on the app side is the same codebase for both. I really can't find the root cause anymore — if anyone knows what's going on, please point me in the right direction.
Also, I'm able to sync/download the StoreKit product configuration file from App Store Connect directly in Xcode, which should also confirm that my App Store Connect backend configuration is correct.