ASP .NET Webhook Receiver

I am trying to create a web app that will receive HTTP Posts containing json. All I want to do for now is show that I can receive the requests. I started by creating an ASP .NET web app with Web API template. I added a controller to receive the posts:

  public class PostmanController : Controller
{

    [System.Web.Mvc.HttpPost]
    public void Index([FromBody] string request)
    {

        // Create handler class object
        PostmanHandler test = new PostmanHandler();

        // Pass request to the convertjsontoobject method
        test.ConvertJsonToObject(request);

    }
}

As you can see here, I also created a handler in the Models folder:

public class PostmanHandler
{
 public void ConvertJsonToObject(string s)
    {
        // Deserialize JSON
        var newData = JsonConvert.DeserializeObject<testobject>(s);
    }
}

Which converts the JSON into a class I made:

public class testobject
{
    public int id { get; set; }
    public string name { get; set; }
}

I am trying to test this out to see if it works but I get a 404 response from Postman when I send a POST request. I am sending it to http://localhost:xxxx/api/Postman which I thought follows the routing in the WebApiConfig file that states: routeTemplate: "api/{controller}/{id}"

Am I leaving out some sort of routing?