Go to the "User Permissions" page within Seller Central, and login to your Amazon seller account as the primary user.

If you haven't signed up for Amazon MWS previously, the "Sign up for MWS" button will appear. Click "Sign up for MWS" if this applies to your account.

If you've already signed up Amazon MWS, click the "Authorize a developer" button.

Check the box to confirm that you want to authorize a developer to access your Amazon seller account with Amazon MWS, and then click the "Next" button.

In the "Developer's Name" text box, enter the name: SELLERCARE

In the "Developer Account Number" text box, enter the MWS developer account identifier: 3196-5523-7372

Once you've entered the information into both text boxes, click the "Next" button.

Copy and paste the account identifiers (Seller ID, Marketplace ID, and MWS Auth Token) that appear on the confirmation screen and email the account identifiers to cs@sellercare.com