我怎么知道使用php的youtube API频道的订阅者数量？

<?php
require_once 'google-api-php-client/vendor/autoload.php';

$client = new Google_Client();
$client->setApplicationName('Your Application Name');
$client->setDeveloperKey('Your API Key');

$youtube = new Google_Service_YouTube($client);

function getChannelSubscriberCount($channelId) {
  global $youtube;
  
  $channelsResponse = $youtube->channels->listChannels('statistics', array(
    'id' => $channelId
  ));

  $channel = $channelsResponse->getItems()[0];
  $subscriberCount = $channel->getStatistics()->getSubscriberCount();

  return $subscriberCount;
}

$channelId = 'YOUR_CHANNEL_ID';
$subscriberCount = getChannelSubscriberCount($channelId);
echo "订阅者数量：" . $subscriberCount;
?>