Product Advertising API
Developer Guide (API Version 2013-08-01)

Associate IDs

To be an Associate, you must sign up in each locale in which you intend to do business. That means, for example, if you have an Associate ID for the US locale, you will not get credit if you submit a PurchaseURL in the DE locale. To get credit, you must get an Associate ID in the DE locale. For more information, see Sign up as an Amazon Associate.