Getting Offer & Plan Details via API

Hello community,

Can anyone offer guidance on how to retrieve details of our Offers and Plans via API request to the Azure Marketplace?

The relevant API's seem to be below https://cloudpartner.azure.com/api/ but, I cannot seem to generate an authentication token that has the correct scope and am receiving 401: Unauthorized. 

e.g. GET: https://cloudpartner.azure.com/api/publishers/{{publisherId}}/offers?api-version=2017-10-31

Steps taken: 

• I already have an operational App Service Principle and can obtain an access token that works with the marketplaceapi.microsoft.com API's (from the Mastering the MarketPlace Saas Accelerator) setup. I can 

• I have granted the App Service Principle the "Manager" role in the Partner Portal as described in the https://learn.microsoft.com/en-us/partner-center/marketplace/cloud-partner-portal-api-prerequisites But, the documentation seems to omit the authentication "scope" I should request in the oAUTH flow. 

Any suggestions or guidance welcomed! Thanks.