Undefined in php query

I do not know why, but it shows me the data correctly in one query and in the other I get the data Undefined !

Showing the following error when going through the for console.log($scope.servicio):

  

Notice : Trying to get property of non-object in /Applications/XAMPP/xamppfiles/htdocs/Paneldetencion/app/php/consultaServicios.php on line 9

  Error querying database.

And when I show only the data console.log(data):

  

Notice : Undefined property: stdClass :: $ service_id in /Applications/XAMPP/xamppfiles/htdocs/Paneldetencion/app/php/consultaServicios.php on line 9
  Error querying database.

The two throw me to the same line the 9: $postdata = file_get_contents("php://input"); The php query is this:

<?php  
    header('Access-Control-Allow-Origin: *');    

    date_default_timezone_set("Chile/Continental");    
    $db = mysqli_connect('localhost','root','','mongos')
    or die('Error connecting to MySQL server.');
    $postdata = file_get_contents("php://input");
    $request = json_decode($postdata);
    $id = $request->id;

    $query = "SELECT identificador, nombre FROM Servicios WHERE id =".$id;
    mysqli_query($db, $query) or die('Error querying database.', error_reporting());

    $result = mysqli_query($db, $query);
    $array = array();
    while ($row = mysqli_fetch_array($result)) {
        $array[] = array(
            $row["identificador"]
           $row["nombre"]
        ); 
    }

   echo $json_info = json_encode($arr);

?>

And the controller is like this:

        $http({
        method: 'POST',
        url: 'http://localhost/Paneldetencion/app/php/consultaServicios.php',  
     //   url: 'php/consultaServicios.php',
        headers: {
            'Content-Type': 'application/json',
            'Accept': 'application/json'
        },

        data:{

          id: 38
        }

    })

.then(function(data) {

    var dat = data.data;

    $scope.servicio = [];
          for (var i = 0; i < dat.length; i++) {

            var datos = {
                nombre: dat[i].nombre,
                identificador: dat[i].identificador,
            };

            $scope.servicio.push(datos);
        } 

        console.log("RESPUESTA: ",$scope.servicio)
});

As I said before, this same query I have it with other data and returns them correctly, but not all the data by the id where. But he shows them. Here all data is Undefined