Amazon FBA Inventory API Authentication

Hi guys,

I am wondering if anyone has had any success with querying the Inventory API in Amazon?
Their Documentation is quite confusing and I am not sure on the steps to authenticate.
I’ve created a security profile in the amazon dev account and have the client id and secret, from which I can call the following endpoint to get a token successfully:

However, when trying to use this token in the following endpoint:

I am getting the " * MissingAuthenticationToken" error.

I want to try and query inventory stock by location.

API Docs here:

Any help to point me in the right direction would be greatly appreciated.

Thanks in advanced!