如何从FB图书馆获得电子邮件id

我想访问用户的电子邮件id，为此我尝试了下面的代码，为此我检查了许多网站。我找到了这些方法来访问用户的电子邮件id。但这些方法似乎都不起作用。请帮我解决这个问题。

提前感谢。

<?php
session_start();
require_once 'autoload.php';
use Facebook'FacebookSession;
use Facebook'FacebookRedirectLoginHelper;
use Facebook'FacebookRequest;
use Facebook'FacebookResponse;
use Facebook'FacebookSDKException;
use Facebook'FacebookRequestException;
use Facebook'FacebookAuthorizationException;
use Facebook'GraphObject;
use Facebook'Entities'AccessToken;
use Facebook'HttpClients'FacebookCurlHttpClient;
use Facebook'HttpClients'FacebookHttpable;
// init app with app id and secret
FacebookSession::setDefaultApplication('MY_app_id', 'my_app_secret');
$helper = new FacebookRedirectLoginHelper('http://prov.resolv.com/provision_sid/Facebook_2/fbconfig.php');
try {
    $session = $helper->getSessionFromRedirect();
} catch (FacebookRequestException $ex) {
} catch (Exception $ex) {
}
if (isset($session)) {
    // graph api request for user data
    $request = new FacebookRequest($session, 'GET', '/me');
    $response = $request->execute();
    // get response
    $graphObject = $response->getGraphObject();
    $fbid = $graphObject->getProperty('id');              // To Get Facebook ID
    $fbfullname = $graphObject->getProperty('name');      // To Get Facebook full name
    echo $femail = $graphObject->getProperty('email'); 
    die();
    $_SESSION['FBID'] = $fbid;
    $_SESSION['FULLNAME'] = $fbfullname;
    $_SESSION['EMAIL'] = $femail;
    /* ---- header location after session ---- */

    header("Location: index.php");
} else {
    $loginUrl = $helper->getLoginUrl();
    header("Location: " . $loginUrl);
}
?>

I tried multiple option to request email id

1> $request = new FacebookRequest($session, 'GET', '/me?fields=name,email');

2> $request = new FacebookRequest($session, 'GET', '/me',['fields' => 'id,name,email,address,first_name,last_name']);

通过上述请求，我无法获得用户的电子邮件id。

是否有其他方法可以请求用户的email id