Php how to add Notify Subscribers when uploading video Youtube Api

I have the below code working perfectly, i use it to upload videos to my youtube channel but i want to add Notify Subscribers everytime i upload new video, what piece of code do i need to add to my code, i did a lot of research online but couldn't find any solution.

<?php/** * Library Requirements * * 1. Install composer (https://getcomposer.org) * 2. On the command line, change to this directory (api-samples/php) * 3. Require the google/apiclient library *    $ composer require google/apiclient:~2.0 */if (!file_exists(__DIR__ . '/vendor/autoload.php')) {  throw new \Exception('please run "composer require google/apiclient:~2.0" in "' . __DIR__ .'"');}require_once __DIR__ . '/vendor/autoload.php';session_start();/* * You can acquire an OAuth 2.0 client ID and client secret from the * {{ Google Cloud Console }} <{{ https://cloud.google.com/console }}> * For more information about using OAuth 2.0 to access Google APIs, please see: * <https://developers.google.com/youtube/v3/guides/authentication> * Please ensure that you have enabled the YouTube Data API for your project. */$OAUTH2_CLIENT_ID = 'xxxxxxx';$OAUTH2_CLIENT_SECRET = 'xxxxxxx';$client = new Google_Client();$client->setClientId($OAUTH2_CLIENT_ID);$client->setClientSecret($OAUTH2_CLIENT_SECRET);$client->setScopes('https://www.googleapis.com/auth/youtube');$redirect = filter_var('http://' . $_SERVER['HTTP_HOST'] . $_SERVER['PHP_SELF'],    FILTER_SANITIZE_URL);$client->setRedirectUri($redirect);// Define an object that will be used to make all API requests.$youtube = new Google_Service_YouTube($client);// Check if an auth token exists for the required scopes$tokenSessionKey = 'token-' . $client->prepareScopes();if (isset($_GET['code'])) {  if (strval($_SESSION['state']) !== strval($_GET['state'])) {    die('The session state did not match.');  }  $client->authenticate($_GET['code']);  $_SESSION[$tokenSessionKey] = $client->getAccessToken();  header('Location: ' . $redirect);}if (isset($_SESSION[$tokenSessionKey])) {  $client->setAccessToken($_SESSION[$tokenSessionKey]);}// Check to ensure that the access token was successfully acquired.if ($client->getAccessToken()) {  $htmlBody = '';  try{    // REPLACE this value with the path to the file you are uploading.    $videoPath = __DIR__ . '/video.mp4';    // Create a snippet with title, description, tags and category ID    // Create an asset resource and set its snippet metadata and type.    // This example sets the video's title, description, keyword tags, and    // video category.    $snippet = new Google_Service_YouTube_VideoSnippet();    $snippet->setTitle("Test title");    $snippet->setDescription("Test description");    $snippet->setTags(array("tag1", "tag2"));    // Numeric video category. See    // https://developers.google.com/youtube/v3/docs/videoCategories/list    $snippet->setCategoryId("22");    // Set the video's status to "public". Valid statuses are "public",    // "private" and "unlisted".    $status = new Google_Service_YouTube_VideoStatus();    $status->privacyStatus = "public";    // Associate the snippet and status objects with a new video resource.    $video = new Google_Service_YouTube_Video();    $video->setSnippet($snippet);    $video->setStatus($status);    // Specify the size of each chunk of data, in bytes. Set a higher value for    // reliable connection as fewer chunks lead to faster uploads. Set a lower    // value for better recovery on less reliable connections.    $chunkSizeBytes = 1 * 1024 * 1024;    // Setting the defer flag to true tells the client to return a request which can be called    // with ->execute(); instead of making the API call immediately.    $client->setDefer(true);    // Create a request for the API's videos.insert method to create and upload the video.    $insertRequest = $youtube->videos->insert("status,snippet", $video);    // Create a MediaFileUpload object for resumable uploads.    $media = new Google_Http_MediaFileUpload(        $client,        $insertRequest,'video/*',        null,        true,        $chunkSizeBytes    );    $media->setFileSize(filesize($videoPath));    // Read the media file and upload it chunk by chunk.    $status = false;    $handle = fopen($videoPath, "rb");    while (!$status && !feof($handle)) {      $chunk = fread($handle, $chunkSizeBytes);      $status = $media->nextChunk($chunk);    }    fclose($handle);    // If you want to make other calls after the file upload, set setDefer back to false    $client->setDefer(false);    $htmlBody .= "<h3>Video Uploaded</h3><ul>";    $htmlBody .= sprintf('<li>%s (%s)</li>',        $status['snippet']['title'],        $status['id']);    $htmlBody .= '</ul>';  } catch (Google_Service_Exception $e) {    $htmlBody .= sprintf('<p>A service error occurred: <code>%s</code></p>',        htmlspecialchars($e->getMessage()));  } catch (Google_Exception $e) {    $htmlBody .= sprintf('<p>An client error occurred: <code>%s</code></p>',        htmlspecialchars($e->getMessage()));  }  $_SESSION[$tokenSessionKey] = $client->getAccessToken();} elseif ($OAUTH2_CLIENT_ID == 'REPLACE_ME') {  $htmlBody = <<<END<h3>Client Credentials Required</h3><p>    You need to set <code>\$OAUTH2_CLIENT_ID</code> and<code>\$OAUTH2_CLIENT_ID</code> before proceeding.<p>END;} else {  // If the user hasn't authorized the app, initiate the OAuth flow  $state = mt_rand();  $client->setState($state);  $_SESSION['state'] = $state;  $authUrl = $client->createAuthUrl();  $htmlBody = <<<END<h3>Authorization Required</h3><p>You need to <a href="$authUrl">authorize access</a> before proceeding.<p>END;}echo $videoPath;?><!doctype html><html><head><title>Video Uploaded</title></head><body><?=$htmlBody?></body></html>

I really appreciate if someone could help.