You can make money when you use the Product Advertising API to advertise Amazon products in conjunction with the Amazon Associates Program. How? You earn referral fees when you join the Amazon Associates program and the users you refer to Amazon sites buy qualifying products.

You need to get an Amazon Associates account and ensure that you include your associate tag in API requests. That way the URLs returned by the API contain your Associate tag and when a user visits an Amazon site through a tagged link and buys a product, the developer earns referral fees. For more information about getting an Amazon Associates account, see Becoming an Associate.