I am investigating a repeatable StoreKit 2 restore failure in SommPal, TestFlight 1.0.0 (20), on a physical iPhone running iOS 26.6.2. Feedback report FB24795995 has been submitted with attachments. An explicit user tap calls try await AppStore.sync(). Apple presents an Apple Account password prompt. The tester enters the password for the displayed account and presses OK; no visible authentication error appears. The call then throws typed StoreKitError.unknown, bridged as NSError domain StoreKit.StoreKitError, code 2. Traversal through NSUnderlyingErrorKey exposes no nested cause. This is not SKErrorDomain code 2, and we are not interpreting it as user cancellation. The tester reports Media & Purchases signed out and a dedicated Sandbox Apple Account configured under Developer settings. The prompt displays the personal Apple Account rather than the dedicated sandbox account. Sandbox subscription management loads successfully. Controlled tests on September 15, 2026: Isolated refresh on Wi-Fi: same unknown error. Normal Restore: available purchases are independently verified by our server and annual access remains active, but explicit Apple sync fails. Isolated refresh on cellular: same error. Full iPhone restart, then isolated refresh on cellular: same error. The isolated test serializes app-initiated StoreKit operations and waits for previous operations to finish. It skips local transaction recovery and acknowledgement before calling sync. Native Transaction.updates observation remains active; we have not isolated Apple internal work. Our native probe imports only Foundation and StoreKit and directly calls AppStore.sync(). It catches StoreKitError.userCancelled separately, then classifies other typed StoreKitError cases and records safe NSError domain/code values. The application uses React Native/Expo with our own Swift bridge. The isolated action performs a server permission check before entering the native restore method. Native entitlements are enumerated only if sync succeeds; the isolated action does not acknowledge or finish transactions. The failure occurs at sync, before that enumeration. We retain signature, ownership and expiration verification. Valid access is not removed solely because sync fails. A previous application-account ownership conflict was separately identified; using the rightful application account restores access but does not resolve this sync failure. We have prepared a dependency-free SwiftUI/Xcode sample containing the same probe, but it has not yet been compiled or tested as a standalone app. We have not reproduced on a second physical device. Automated error-mapping tests pass but do not establish that real Apple authentication works. We are not claiming a confirmed iOS defect. What supported diagnostic step, logging profile, call context, or integration change would help distinguish an integration problem from an account/device/service issue? Is the personal-account prompt expected in this TestFlight configuration? Additional private diagnostics can be supplied through FB24795995. The attached screenshot shows the isolated failure after restarting the iPhone.