To take advantage of this sale, go here and click on the book you want. You'll see a button "Buy with coupon," which should automatically get you the discount price.
By the way, the paperback of Busara Road, currently a finalist for two major awards, is being heavily discounted by Amazon, which thinks it has too many copies. Though we don't usually urge readers to buy from Amazon, in this case we'd love to prove them wrong.
Stay safe and read a lot!