PA API 5 for New Associates
Before you register for the Product Advertising API, you must have Amazon Associates account that has been reviewed and received final acceptance into the Amazon Associates Program.
If you do not have an Amazon Associate account, you must sign up for Amazon Associates. For more information, see Sign up as an Amazon Associate.
Product Advertising API sign up is available only to associates who have referred qualified sales and have been accepted into the program.
You can follow this official guide from Amazon in order to sign up for the PA API 5!