WCF Duplex Communication in Windows Service

namespace WindowsServiceApp
{

    [ServiceContract(CallbackContract = typeof(IWcfServiceCallBack))]
    public interface IWcfService
    {
        [OperationContract]
        void getAuth(string auth);
        [OperationContract]
        double getPrice(string auth);
    }
    [ServiceContract]
    public interface IWcfServiceCallBack
    {
        [OperationContract(IsOneWay = true)]
        void getCallBack(string returnAurth);
    }
}


namespace WindowsServiceApp
{

    public class WcfService : IWcfService
    {
        
        public static string errorMessage = "";
        public void getAuth(string auth)
        {
            WindowsServiceApp.WinService.FormScan formScan = new WinService.FormScan();
         
        }

        public double getPrice(string auth)
        {
            double a = 1;
            return a;
        }

    }
}


namespace WindowsServiceApp
{
    public partial class WinService : ServiceBase
    {
        ServiceHost host;
        private static string errorMessage = "";
        public WinService()
        {
            InitializeComponent();
        }

        protected override void OnStart(string[] args)
        {
            host = new ServiceHost(typeof(WcfService));
            host.Open();
        }

        protected override void OnStop()
        {
            host.Close();
        }
     }
}




<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <system.serviceModel>
    <behaviors>
      <serviceBehaviors>
        <behavior name="WindowsServiceApp.WcfServiceBehavior">
          <serviceMetadata httpGetEnabled="true" />
          <serviceDebug includeExceptionDetailInFaults="true" />
        </behavior>
      </serviceBehaviors>
    </behaviors>
    <bindings>
      <wsDualHttpBinding>
        <binding name="WSDualHttpBindingConfig"
          clientBaseAddress="http://localhost:8733/" >
          <security mode="None"/>
        </binding>
      </wsDualHttpBinding>
    </bindings>
    <services>
      <service behaviorConfiguration="WindowsServiceApp.WcfServiceBehavior"  name="WindowsServiceApp.WcfService">
        <endpoint address="" binding="wsDualHttpBinding" bindingConfiguration="WSDualHttpBindingConfig"  contract="WindowsServiceApp.IWcfService" />
        <endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange" />
        <host>
          <baseAddresses>
            <add baseAddress="http://localhost:8733/" />
          </baseAddresses>
        </host>
      </service>
    </services>
  </system.serviceModel>
</configuration>