Could you provide more details and context for your issue please? This is using a 3rd party API so it’s best to include the link to the documentation at the very least.
This might need you to contact thier support team for more information, Postman is working as expected and the server is returning that response.
It could be a limitation for your token as it also mentions OAuth in the error - I don’t know that API and if specific permissions are given/not given for certain users.