Access is Denied when calling /agreements Adobe Sign API in Postman

We are currently evaluating the Adobe Sign APIs capabilities for a requirement and we are getting an Access is Denied error when invoking the /agreements API via Postman. We intend to invoke all of the APIs programatically so we are using the Integration Key (with all scopes checked) for the Authorization header.

However, if we invoke the same API through Swagger, it returns successfully.

We are able to call the POST /agreements API without issues.