We operate the same process as ProtectAir and PeteB we only use MWS to import all the orders into Sage 200, Magento for the Site. We used a developer to do this.
I presume from the OP the issue is you, the Seller trying to register as a developer, this on the basis you actually want to develop your own MWS Application for Amazon or an Amazon Seller? Amazon have strict criteria to be a MWS developer, I would presume you actually want to authorise your Seller account
I want to access my own Amazon seller account with MWS.— Select this option when you sign
up to use Amazon MWS for your own Amazon seller account, Amazon MWS will assign a developer
account identifier to you. When you make Amazon MWS requests, you’ll use the developer account
credentials that are associated with your developer account, plus the Merchant ID and the Marketplace
ID for your seller account.
Developing an Amazon MWS application
To create applications that use Amazon MWS, you need a development environment for Java, C#, or
PHP. If you are a developer who is using Amazon MWS to build software for your own eligible Amazon
account, use the email address for that Amazon seller account when you sign up for Amazon MWS,
selecting the option to use your own Amazon MWS-eligible seller account with Amazon MWS. For
more information, see the topic Signing Up for Amazon MWS. If you are a developer who wants to
use Amazon MWS to build professional software for other eligible Amazon sellers, you must first sign
up for Amazon MWS with your own Amazon MWS-eligible seller account. On the last page of your
Amazon MWS registration, make note of your developer account identifier, as you’ll need to provide
this number to sellers who want to use your developer services or application.
When your software is ready for testing with additional seller accounts, you can provide sellers with
your developer account identifier, which they can use to register forAmazon MWS. The sellers log into
their ownAmazon MWS-eligible seller accounts and insert your developer account identifier during the
registration process. The sellers need to make note of the Merchant ID and Marketplace ID for their
accounts, and pass that information to you.You will then be able to make Amazon MWS requests on
their behalf, using their seller credentials and your developer credentials.
For further assistance with building your application, we suggest you use the other available resources
for Amazon MWS. For more information, see Related Resources
I want to use an application to access my Amazon seller account with MWS.— Select this option
if you want to use an application to access your Amazon seller account using Amazon MWS. When
you register, you must enter the developer account identifier for the application you will be using. The
final page of the Amazon MWS registration process shows your Merchant ID and Marketplace ID.You
will use these identifiers in the application you will use.
I want to give a developer access to my Amazon seller account with MWS.— Select this option
when you want to authorize a third-party developer to access your account with Amazon MWS.