All you need to do is follow the below step and hopefully will be able to buy goodybag from credit:
1. Log in to your account
2. Go to the top-up section
3. Click "Select" on "goodybags"
4. Click 'Select' on the applicable purchase that you want to add to your account.
5. The goodybag will show on the right hand side. Review your basket again, then click "Continue"
6. Click the 'Exchange airtime credit' button at the top of the page - this will confirm your order.
Please note that you can buy goodybag equivalent to credit or less than that. So, before buying a goodybag always check the balance by dialing *100# on your phone.
You can check your payment history from your dashboard here