Can't use in-app purchase: This is not a test user account

Receiving an error message like this? It turns out that this error is caused by an app called AppSync for those who jailbreak their device.

To enable in-app purchase again, follow these steps:

1. Uninstall AppSync from Cydia.
   
2. Uninstall Boxcar.
   
3. Reboot your device.
   
4. Re-download Boxcar from the appstore
   
5. Make the in-app purchase
   
6. (Optional) you can then reinstall AppSync