Fix Flutter In-App Purchase

My Flutter app is live on Google Play and almost ready for submission to the App Store, but the in-app purchase flow stalls before the transaction is confirmed. No items are delivered and no revenue is recorded, so users simply abandon the process. I have not set up purchases anywhere else yet, so this Android build is our only reference point.

What I need from you is a concise, reliable fix that lets a user tap “Buy”, run through Google Play Billing (and soon StoreKit), and immediately receive their product without errors or timeouts. The project is written in Dart and currently relies on the in_app_purchase package; feel free to recommend a version bump or alternative approach if that speeds up certification on both stores.

Deliverables
• Diagnose why “Purchase not completing” occurs on the current Android build (review logs, callbacks, pending states, signature validation, etc.).
• Implement and test the working flow on Android; then prepare the same code path for iOS so I can submit confidently to the App Store.
• Provide clear setup notes or code comments so I can replicate the steps in future releases.

A quick turnaround is ideal because the iOS launch is waiting on this single blocker. Let’s get users paying—and receiving—without a hitch.