on /api in browser you’d expect to see 400 with
{ "error": { "message": "The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed. Check the \"access token\" parameter.", "code": 400, "data": [] } }
I’ve seen one similar problem, also with IIS, could you take a look at those posts and see if it helps with your problem? API Call through Postman