Amazon offers a $10 Amazon Digital Credit for free when you open an Amazon Cash account with $50. This is a new service that lets you use cash to shop on Amazon. When you open an account, you'll receive a barcode (via text, the Amazon App, or to print at home), which you can bring to participating stores to add funds to your Amazon Balance. (Your Amazon Balance also includes gift card redemptions.)
Note that the promotional credit can only be used on items in the Appstore, Kindle books, or digital video, music, software, and video games.