Click Sign up for MWS and then log in to your MWS account – or register if you don’t have a MWS account (you must have a Amazon Pro Seller account to register with MWS). Note, if it’s your first time registering, on your first login it may send you to your Amazon seller account; if this happens, just go back to the “Sign up for MWS” button using the link above and it will redirect you to the page displayed below:
Select ‘I want to use an application to access my Amazon seller account with MWS.‘ as shown by the screenshot below. Application name: GroovePacker Input ONE of the two developer account numbers below, depending which locale you are using… Developer account number: 1512-6494-8396 Click Next.
Agree to the terms on the next page to continue.
Copy & save your ‘Seller ID’ and ‘MWSAuthToken’. You also need your Marketplace ID, and Seller ID.