Query WebApi with json object from Angular ngResource

I have a simple WebApi that I'd like to connect to an angularjs app

The api looks something like this

public HttpResponseMessage GetSokAvtal(SokAvtalAdvanced sokAvtalAdvanced)
{
    if (sokAvtalAdvanced != null && sokAvtalAdvanced.IsValid())
    {
        try
        {
            var avtal = db.spSokAvtalAdvanced(
                limit: sokAvtalAdvanced.Limit,
                offset: sokAvtalAdvanced.Offset);

            return Request.CreateResponse(HttpStatusCode.OK, avtal);
        }
        catch (Exception ex)
        {
            return Request.CreateErrorResponse(HttpStatusCode.InternalServerError, "Ett fel har inträffat");
        }
    }

    return Request.CreateErrorResponse(HttpStatusCode.BadRequest, "Felaktiga parametrar");
}

The SokAvtalAdvanced looks like this

public class SokAvtalAdvanced
{
    #region Properties

    private int _limit;
    public int Limit
    {
        get { return _limit > 0 && _limit < 50 ? _limit : 10; }
        set { _limit = value;  }
    }

    private int _offset;
    public int Offset
    {
        get { return _offset > 0 ? _offset : 0; }
        set { _offset = value; }
    }

    #endregion

    #region Methods

    /// <summary>
    /// Returns a valid modelstate
    /// </summary>
    /// <returns></returns>
    public bool IsValid()
    {
        return true;
    }

    #endregion

}

To map this to angular I've done this so far without any luck

app.controller("SokAvtalController", ['$scope', 'SokApi', function ($scope, SokApi) {
    $scope.avtal = SokApi.query({ sokAvtalAdvanced: {
            "Limit": 10,
            "Offset": 0
    }});

    console.log($scope.avtal);

    $scope.SelectGroup = function (avtal) {

    };
}]);

angular.module('app.avtalsportalen', ['ngResource'])
    .factory('SokApi', ['$resource', function ($resource) {
        return $resource('/api/SokAvtal/:sokAvtalAdvanced');
    }]);

Any idea of what's wrong with my call? The SokAvtalAdvanced sokAvtalAdvanced is null in WebApi every call

Thanks