I'm developing an application for a seller at Amazon, using Marketplace Web Service API (MWS). The seller has created an account for managing his inventory, and says that he assigned the necessary permissions. However, clicking "Sign up for MWS" button on https://developer.amazonservices.com/ results in permission error: "Insufficient user rights." Can anyone clear up what permission(s) Amazon Marketplace requires for accessing their API, or at least provide a list of all possible permissions?
I found the answer. It has actually turned out that you can't sign up for Amazon MWS from a sub-account. No such permission exists, so this must be done by the owner.