Send Zebra TC26 ZPL Android Studio via Bluetooth to ZD420

Question

I try to send command to ZD420 from Zebra TC26 app. I create app with android studio but i have error and not send command

I use zebra library

My Code :

                   val bAdapter: BluetoothAdapter = BluetoothAdapter.getDefaultAdapter()
                    for (device in bAdapter.bondedDevices) {
                        sendZplOverBluetooth(device.address.toString())
                    }

private fun sendZplOverBluetooth(theBtMacAddress: String) {
        try {
            val thePrinterConn: Connection = BluetoothConnection(theBtMacAddress)
            thePrinterConn.open()
            if (thePrinterConn.isConnected) {
                val zplData = "^XA^FO20,20^A0N,25,25^FDThis is a ZPL test.^FS^XZ"
                thePrinterConn.write(zplData.toByteArray())
                thePrinterConn.close()
            }
        } catch (e: java.lang.Exception) {
            e.printStackTrace()
        }
    }

Error :

W/System.err: com.zebra.sdk.comm.ConnectionException: Could not connect to device: read failed, socket might closed or timeout, read ret: -1
W/System.err:     at com.zebra.sdk.comm.ConnectionA.throwAsConnectionException(Unknown Source:42)