When you check out, you'll be brought to the following page on the web app:
On the mobile app, you will follow the same initial steps but once you get to the check out page, you'll need to look at the top, right corner where it says "Add Code". Once you click on that, it will bring down a drop down screen for you to enter your promo code!
Please note that you can only add one promo code at a time BUT you can still use multiple book credits on your purchase.
If you have any trouble adding your promo code, please reach out to our Support team at firstname.lastname@example.org and one of our agents would be happy to help you out!