ReshSharp / ASP.NET WebAPI - Using POST with url parameters

I've the following ASP.NET WebAPI binding:

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

And my Controller looks like this:

public class ReferenceDataController : BaseController
{
    [RequireUserToken(ApprovedDeviceToken = true, ValidUserToken = true)]
    [HttpPost]
    public IEnumerable<SynchronizeItem<IReferenceDataItem>> Sync([FromBody]IEnumerable<SynchronizeItem<IReferenceDataItem>> clientSyncItems, [FromUri]int referenceDataType)
    {
        // my code
    }

On the client site I use the following code to send a request:

var client = new RestClient (baseUrl);
var request = new RestRequest (resource, method);
request.XmlSerializer = new JsonSerializer ();
request.RequestFormat = DataFormat.Json;
request.AddHeader ("X-Abc-DeviceToken", deviceToken);

if (!string.IsNullOrWhiteSpace (userToken))
    request.AddHeader ("X-Abc-UserToken", userToken);

if (payload != null)
    request.AddBody (payload);

if (parameters != null) 
{
    foreach (var parameter in parameters)
    {
        request.AddUrlSegment(parameter.Key, parameter.Value);
    }
}

var response = client.Execute<T> (request);

My expectation is, sending a POST request to http://myhost/api/referencedata/sync?referencedatatype=countries with a body which contains an IEnumerable. If I remove the UrlSegment parameters on client site and the second argument on the webservice site, than it works.

How can I combine a body with payload and additional URL parameters?