Nothing obvious is standing out. Based on the documentation and example.
This might be something to post on a SAP forum as it seems related to the specific API.
Its a bit strange that its returning an XML response, and its also referencing Microsoft.
I would maybe double check the authentication to ensure you have the correct authentication type for this service (although I would expect that to produce a different status code).
Can you get any of the other services working? Is there a simpler service that doesn’t use a query filter that you could try? Just to prove the authentication is working properly.