Yes, I fixed it. Root Cause: The unexpected behavior happens because the application window was being closed before the OS purchase dialog could fully initialize. Because there was no active window on the screen, the system dialog had no parent window to anchor ("hook") to, causing the process to fail. The Fix: To fix this, ensure your application window stays open until the purchase flow is entirely complete. Correct Workflow: Open your custom purchase/store window. The user clicks "Buy". Do not close or hide your purchase window yet. Let the OS system dialog appear directly on top of it. Wait for the user to either complete the purchase or cancel it. Once the billing API returns the final success or failure callback, you can safely close your purchase window.