Unable to print text in IMZ320 bluetooth printer using LinkOS Xamarin IOS

I use Zebra IMZ320 bluetooth printer and I try to print text via LinkOS.Plugin in Xamarin IOS. But its unable to print using the sample code which you gave.http://techdocs.zebra.com/link-os/2-13/xamarin/

I have attached my code and error herewith.

public void SendTotalPrint()

        {

            string message = "";

            IConnection connection = null;

            connection = ConnectionBuilder.Current.Build("BT:XXXXJ165202255");

            //await Task.Run(() => {

            connection.Initialize("BT:XXXXJ165202255");

            connection.TimeToWaitAfterWrite = 4000;

            IDiscoveryEventHandler handler = DiscoveryHandlerFactory.Current.GetInstance();

            handler.OnDiscoveryError += DiscoveryHandler_OnDiscoveryError;

            handler.OnDiscoveryFinished += DiscoveryHandler_OnDiscoveryFinished;

            handler.OnFoundPrinter += DiscoveryHandler_OnFoundPrinter;

            BluetoothDiscoverer.Current.FindPrinters(null, handler);

            try

            {

                connection.Open();

                IZebraPrinter printer = ZebraPrinterFactory.Current.GetInstance(PrinterLanguage.ZPL, connection);

                string pl = printer.PrinterControlLanguage.ToString();

                string zpl = "^XA^POI^MNN^LL90^PW400^FO20,20^A0N,50,50^FDTEST^FS^XZ";

                connection.Write(Encoding.UTF8.GetBytes(zpl));

            }

            catch (Exception e)

            {

                message = "Exception: " + (e.Message);

            }

            finally

            {

                if ((connection != null) && (connection.IsConnected))

                {

                    connection.Close();

                }

            }

        }

Error occur in connection.Write(Encoding.UTF8.GetBytes(zpl)); as

{LinkOS.Plugin.ConnectionException: Error writing to connection

  at LinkOS.Plugin.ConnectionImplementation.Write (System.Byte[] data) [0x00052] in <5ba493cd13a6476cb6f38f54ba338afd>:0

  at ZSD.iOS.Interfaces.TotalPrint.SendTotalPrint () [0x000b5]}

I tried both Xamarin PCL and Xamarin.Ios project