Launch the App
On the footer of the App, click on "Account".
Go to Balance and click "Refill" to recharge your account

We have a list of other refill/Payment options here if you can't refill with your card)
Go back to "Store" after a successful refill to purchase your desired book by clicking on the "price icon" close to the book.

If you paid in-app and was not credited, please click here