Register a success for Public Amazon Seller Central's App for SP-API (need a quick fix)

I already have an Amazon Central and Amazon Developers accounts, I want to an Amazon seller partner app that can allow me to access client's sellers account using SP-API after client authroised it from their account. So far I already have set most of them but seems to be getting MD9000 error when client try to approve me in their seller's account.

I need someone who has the experience of registering an SP-API app in Amazon's Seller Central under "Develop Apps" section.