Fix In-App Coin Purchase Bug

My iOS app’s in-app purchase flow is failing: users pay for coin packs but nothing is delivered and an error message appears instead. I need someone who knows StoreKit inside out to trace the problem, squash it, and make sure every successful transaction immediately credits the correct coin amount.

Here’s what I can tell you so far:
• The issue is limited to the iOS build of the mobile app; Android is unaffected.
• Apple’s purchase sheet completes, but the callback that should unlock the product never seems to fire, and a generic error message pops up.
• TestFlight and production builds behave the same.

What I expect from you:
1. Diagnose the root cause in the current Xcode project.
2. Implement a reliable fix (code plus any required App Store Connect or provisioning changes).
3. Provide a quick sanity suite or clear steps I can repeat to verify the coins appear instantly after purchase.
4. Supply a concise summary of the changes so I can include them in the next release notes.

If you’ve recently worked with StoreKit 2 or have shipped live apps with non-consumable or consumable item handling, this should be straightforward. Let’s get those coins flowing again.