I am required to write an Excel Macro to get order and inventory details for my client (using Amazon MWS).
But my client needs my developer ID to grant me access to his account.
I searched a lot but didn't find any link where I can register as a developer and get my Amazon Developer Identifier.
From where I can register as developer and get my developer ID?
Reference: https://developer.amazonservices.ca/gp/mws/faq.html#developForSeller
Answer
You can find your developer ID using the "Sign up for MWS" wizard located here: https://sellercentral.amazon.com/gp/mws/registration/register.html
You will need to have a seller account on the "Professional" plan or higher. If you don't already have one, you can sign up here: http://www.amazon.com/gp/seller-account/mm-summary-page.html
Note that this will only work for vendors on the American version of Amazon - if your client is selling on one of the localized Amazon sites like Amazon.ca, then you will need a developer ID and seller account from the localized sites. In the case of Europe, a European account can authorize any other European account (e.g. a UK seller can authorize a French Amazon account.)