Go to developer.amazonservices.com and click on Sign up for MWS
From the new page, choose the third option - I want to give a developer access to my Amazon seller account with MWS.
Fill in the following information:
Developer's Name: PNPLINE
Developer Account Number: Contact PNPLINE for this info
When complete, click next
Check the two boxes in the page to state that you agree to the terms and conditions from Amazon Marketplace Web Service (Amazon WMS) and click next.
Take note and e-mail the following three information to firstname.lastname@example.org:
1. Seller ID
2. Marketplace ID
3. MWS Auth Token ID
And you're done! You have given PNPLINE access to your Amazon Seller Central account and integration is now complete. Your Amazon FBA shipping and logistics have just become simpler through the B2B system integration.