Closing the app and attempting the purchase again can help to resolve this problem:
- Close the app by clicking the round home button on your device.
- When you're back at your device's home screen, double-click the home button.
- In the menu at the bottom, tap and hold the MindSnacks icon.
- Tap the minus sign to close the app entirely.
- Click the home button again, and then once more to return your home screen.
- Open up MindSnacks and try to purchase again.