Facebook PHP SDK 4.0 get long lived session/token for manage_pages

<?php

$appid = ''; // your AppID
$secret = ''; // your secret

// init app with app id (APPID) and secret (SECRET)
FacebookSession::setDefaultApplication($appid ,$secret);
 
$session = new FacebookSession($_SESSION['demo_accessToken']);
$session_long_lived = $session->getLongLivedSession($appid, $secret);

$request = new FacebookRequest(
 $session_long_lived,
 'GET',
 '/me/accounts'
);
$response = $request->execute();
$graphArray = $response->getGraphObject()->asArray();

get it~ You can check it by Facebook debug tools