Error in Codeigniter REST

I have the following error

{
    "": "Unknown method"
}

my controller Orders :

<?php


defined('BASEPATH') OR exit('No direct script access allowed');
require APPPATH . 'libraries/REST_Controller.php';

class Orders extends REST_Controller {

    public function __construct() {

        parent::__construct();

    }

    public function index_get(){
        echo "probando";
    }


}

Access:

demo/index.php/orders

Routes

$route['Orders']['get'] = 'orders/index';

Does anyone know what is due?