Facebook哈希标签源PHP cURL

如何使用Facebook Graph API获取Facebook标签提要？我想获取特定#HashTag的所有帖子。

我尝试了以下代码：

<?php
  $keyword = '#TagName';
  $graph_url = "https://graph.facebook.com/search?type=post&access_token=xxx&q=$keyword";
  $ch = curl_init();
  curl_setopt($ch, CURLOPT_URL, $graph_url);
  curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
  curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
  curl_setopt($ch, CURLOPT_HEADER, 0);
  curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
  $result = curl_exec($ch);
  curl_close($ch);
  var_dump($result);
?>

但它返回一个错误：

string(82) "{" error":{"message":"No node specified","type":"GraphMethodException","code":100}}"

授予的权限：read_stream

有什么解决办法吗？感谢