Once you have signed up for Amazon Merchant Account you need to associate your Amazon account with Koongo:
A seller must authorize a developer to make calls to Amazon MWS on the seller's behalf.
1. Go to the User Permissions page in Seller Central and log into your Amazon seller account as the primary user. Click Visit Manage Your Apps button
2. Click Authorize new developer button.
3. In the Developer name text box, enter Koongo as the name of the developer that you are authorizing.
4. In the Developer ID text box:
5. In step 2, click the Authorize developer button.
6. The seller's ID and MWS Auth Token appears.
7. IMPORTANT: As a final step, it is necessary to enter Seller ID and MWS Auth Token in Amazon channel detail in Koongo interface. See image below.
Steps are also described at section Authorizing a developer at http://docs.developer.amazonservices.com/en_US/dev_guide/DG_Registering.html