ASP.NET Web API post method parameter is always null

This is my models class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace Test.Models
{
    public class User
    {
        public int Id { get; set; }
        public string Name { get; set; }
        //public DateTime startTime { get; set; }
        //public DateTime endTime { get; set; }
        //public int Age { get; set; }
        //public string Adress { get; set; }
    }
}

This is my controller class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;
using Test.DBA;
using Test.Models;

namespace Test.Controllers
{
    public class UserAPIController : ApiController
    {
        ApiDbContext dbContext = null;
        public UserAPIController()
        {
            dbContext = new ApiDbContext();
        }
        [HttpPost]
        public IHttpActionResult InsertUser(User user)
        {
            dbContext.Users.Add(user);
            dbContext.SaveChangesAsync();

            return Ok(user.Name);
        }

        public IEnumerable<User> GetAllUser()
        {
            var list = dbContext.Users.ToList();
            return list;
        }

        [HttpPost]
        public IHttpActionResult DeleteUser(User user)
        {
            dbContext.Users.Remove(user);
            dbContext.SaveChanges();

            return Ok(user.Name);
        }

        [HttpGet]
        public IHttpActionResult ViewUser(int id)
        {
            var student = dbContext.Users.Find(id);
            return Ok(student);
        }

        [HttpPost]
        public IHttpActionResult UpdateUser(User user)
        {
            User std = dbContext.Users.Find(user.Id);

            std.Name = user.Name;
            //std.startTime = user.startTime;
            //std.endTime = user.endTime;
            //std.Age = user.Age;
            //std.Adress = user.Adress;

            dbContext.Entry(std).State = System.Data.Entity.EntityState.Modified;
            dbContext.SaveChangesAsync();

            return Ok();
        }
    }
}

I'm trying to call the post method with the google chrome app Postman. I call it with raw JSON body:

{
    Id : 1,
    Name : "Sample"
}

The get methods work, but when i debug post methods the parameters are always null.

Edit 1: Routing:

config.Routes.MapHttpRoute(
              name: "DefaultApi",
              routeTemplate: "api/{controller}/{action}/{id}",
              defaults: new { id = RouteParameter.Optional }
          );