Hi,
First, the Smart Accounts and Licensing API is not a Support API - you may have better luck following the Support instructions for the API.
But I don't think tokens generated on production cloudsso.cisco.com token server will work on the stage API proxy at apmx-stage.cisco.com. The Code Snippets section of the Smart Accounts and Licensing API point to apx.cisco.com. Perhaps you'll have better luck using the prod API service.
But again, the Smart Accounts and Licensing API support team will be better able to help you out.
Regards,
Keith