Readers class doesn´t found a device

Hello,

I´m trying to connect to RFID Reader 8500 through "RFIDAPI3Library" but when I use the Class Readers it doesn´t found any device.

My code is like this:

import android.os.AsyncTask;

import android.support.v4.app.Fragment;

import android.support.v7.app.AppCompatActivity;

import android.os.Bundle;

import com.zebra.rfid.api3.ENUM_TRANSPORT;

import com.zebra.rfid.api3.InvalidUsageException;

import com.zebra.rfid.api3.OperationFailureException;

import com.zebra.rfid.api3.ReaderDevice;

import com.zebra.rfid.api3.Readers;

import java.util.ArrayList;

import com.zebra.rfid.api3.RFIDReader;

public class MainActivity extends AppCompatActivity implements Readers.RFIDReaderEventHandler {

   @Override
   protected void onCreate(Bundle savedInstanceState) {

   super.onCreate(savedInstanceState);

  setContentView(R.layout.activity_main);

  Readers readers= new Readers(this, ENUM_TRANSPORT.BLUETOOTH);

(I change this variable to "ENUM_TRANSPORT.SERVICE_SERIAL" but it throw another Exception)

  ArrayList<ReaderDevice> availableRFIDReaderList = null;

   try {

  availableRFIDReaderList = readers.GetAvailableRFIDReaderList();

  ReaderDevice readerDevice = availableRFIDReaderList.get(0);

  RFIDReader rfidReader = readerDevice.getRFIDReader();

  rfidReader.connect();

  } catch (InvalidUsageException e) {

  e.printStackTrace();

  } catch (OperationFailureException e) {

  e.printStackTrace();

  }catch (RuntimeException e){

  e.printStackTrace();

  }

  }

   @Override
   public void RFIDReaderAppeared(ReaderDevice readerDevice) {

  }

   @Override
   public void RFIDReaderDisappeared(ReaderDevice readerDevice) {

  }

}

With ENUM_TRANSPORT.BLUETOOTH it founds zero device

With ENUM_TRANSPORT.SERVICE_SERIAL it throw "RFID service is not installed or available Failure in resolving dependency"

The Zebra RFID Reader device is already paired with the phone.

Please, I need some help because is hard to find solutions about this on web and when I run the program in the app "Zebra RFID API Mobile"  it throws the same Exception.

Thank you very much for your answers.