Minimum-viable StoreKit 2 reference app. Live on the App Store.
TipJar is the smallest possible in-app purchase demo: five Swift files, three tip-amount buttons, full StoreKit 2 purchase + restore + transaction-listener pipeline. The teaching example for the book's controls chapter (Book 06) and error-handling chapter (Book 18, three layers of error feedback). One screen, no settings, no navigation — the buttons are the app.
Full Shop Manual → GitHub Repository
Email michael@fluharty.com with a description of the issue, the device you're on, and the version number from the App Store.