How can I resolve this issue with Authenticating to the Marketplace SaaS Fulfillment API?

@Robert Winger welcome to the Microsoft Q&A community.

It sounds like your authentication token is valid but missing the correct audience or Entra app ID, which is causing the Marketplace SaaS Fulfillment API to reject it. Here are a few things you can check:

1. Ensure the correct audience (aud) claim – The token must include the correct audience value that matches the API you are trying to access. Verify that the aud claim in your token matches the expected value for the Marketplace API.
2. Confirm the Entra app ID – The API might be expecting a specific Entra app ID in the token. Double-check that your app registration is correctly configured and that the token includes the right app ID.
3. Use the correct endpoint for token acquisition – Make sure you are requesting the token from the correct OAuth endpoint that is intended for Marketplace API authentication.
4. Check API permissions – Your app registration should have the necessary permissions to access the Marketplace API. Ensure that the required API permissions are granted in Microsoft Entra ID.
5. Validate the token with Microsoft documentation – You can compare your token structure with examples provided in Microsoft's official documentation to ensure it meets the expected format.

You might find additional insights in discussions on Microsoft Q&A or Stack Overflow

I hope these helps. Let me know if you have any further questions or need additional assistance.

Also if these answers your query, do click the "Upvote" and click "Accept the answer" of which might be beneficial to other community members reading this thread.

I have the same question!

The authorization token included in the request is valid, however it does not include the correct audience or the entra app id.

https://learn.microsoft.com/en-us/partner-center/marketplace-offers/pc-saas-registration

https://learn.microsoft.com/en-us/partner-center/marketplace-offers/pc-saas-fulfillment-subscription-api#resolve-a-purchased-subscription

Target resource for which the token is requested with a default scope. Use 20e940b3-4c77-4b0b-9a53-9e16a1b010a7/.default because Marketplace SaaS API is always the target resource in this case.