Please perform some troubleshooting steps to avoid any errors with the in-game purchases:
- Check the quality of your connection, and make sure it's stable.
- Check if your payment method is complete
- Make sure the Date and Time are correct and correspond to your local time zone.
- Make sure your game and software are up to date.
- Log out and Log in Back to your Play Store account.
- Restart the Device.
The above steps should help you to minimize the possibility of payment errors.