Privacy policy.
Digital products have a number of special characteristics that need to be taken into consideration when you're selling them to your customers.
A digital product - such as a song download or an app download - cannot be returned.
And many digital products (or digital apps) allow interaction between users and collect user information when the user engages with the product.
This is what a SaaS app does: it collects data from users, but it requires a subscription from its customers, unlike a digital product/app that generally don't require ongoing subscriptions.
As a result, the nature of selling digital products creates unique legal considerations that are covered by your legal agreements.