Particular field getting NULL after form post

Hi I'm using Angulajs as front end and ASP.NET WebAPI as backend.

This is my Model class:

 public class UserModel
 {
    [Required]
    [Display(Name = "User name")]
    public string UserName { get; set; }

    [Required]
    [StringLength(100, ErrorMessage = "The {0} must be at least {2} characters long.", MinimumLength = 6)]
    [DataType(DataType.Password)]
    [Display(Name = "Password")]
    public string Password { get; set; }

    [DataType(DataType.Password)]
    [Display(Name = "Confirm password")]
    [Compare("Password", ErrorMessage = "The password and confirmation password do not match.")]
    public string ConfirmPassword { get; set; }

    [Required]
    [StringLength(50, ErrorMessage = "The {0} must be at least {2} characters long.", MinimumLength = 7)]
    [Display(Name = "Email")]
    public string Email { get; set; }

    [Required]
    [Display(Name = "Phone")]
    public string PhoneNumber { get; set; }


 }

Controller:

// POST api/Account/Register
        [AllowAnonymous]
        [Route("Register")]
        public async Task<IHttpActionResult> Register(UserModel userModel)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            IdentityResult result = await _repo.RegisterUser(userModel);

            IHttpActionResult errorResult = GetErrorResult(result);

            if (errorResult != null)
            {
                return errorResult;
            }
            return Ok();
        }

This is my Angular Service:

var _saveRegistration = function (registration) {

return $http.post('http://localhost:26264/api/account/register', registration).then(function (response) {

       return response;
 });
};

I'm sending payload P.S This is made up payload

registration:{
    userName:"UserName",
    email: "eamil@emal.com",
    password:"password",
    confirmPassword:"password",
    phone: "9898989898"
  }

When I debug I see all the values in payload but when I set debugger at API Controller "register" method field "PhoneNumber" is null. I don't know what wrong I'm doing, please help

via Chebli Mohamed