Facebook SDK返回错误：您必须提供访问令牌。 Php Facebook Api

Question

<?php

require_once 'Facebook/autoload.php';
require_once 'Facebook/Authentication/AccessToken.php';
$fb = new Facebook\Facebook([
  'app_id' => '2452542542fsrgrgrg',
  'app_secret' => '5245dffhdhr5535353535',
  'default_graph_version' => 'v2.2',
  ]);

$linkData = [
  'link' => 'http://www.example.com',
  'message' => 'User provided message',
  ];
$helper = $fb->getRedirectLoginHelper(); 
try {
  $accessToken = $helper->getAccessToken(); 
  // Returns a `Facebook\FacebookResponse` object
  $response = $fb->post('/me/feed', $linkData, $accessToken);
} catch(Facebook\Exceptions\FacebookResponseException $e) {
  echo 'Graph returned an error: ' . $e->getMessage();
  exit;
} catch(Facebook\Exceptions\FacebookSDKException $e) {
  echo 'Facebook SDK returned an error: ' . $e->getMessage();
  exit;
}

$graphNode = $response->getGraphNode();

echo 'Posted with id: ' . $graphNode['id'];

?>

我收到此错误“Facebook SDK返回错误：您必须提供访问令牌。”我试图搜索，我没有任何可靠的答案。任何有想法的人都可以分享。