How to insert featured comments with Youtube API - youtube-api

Question

I'm inserting videos on youtube using API in PHP version. But I'm not able to include a highlight comment in the videos. In the youtube documentation the example is in json , and as I'm doing it in php it just doesn't work.
See part of my code is like this:
// 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();
$snippet->setTitle("Cats are cute #".$filme['Data ID']);
$snippet->setDescription($filme['titulo']);
$snippet->setTags('cats','cutecats','cute');
// Numeric video category. See
// https://developers.google.com/youtube/v3/docs/videoCategories/list
$snippet->setCategoryId("19");
// 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);
And the youtube suggestion to include comments using the API is this:
{
"snippet": {
"channelId": "UC_x5XG1OV2P6uZZ5FSM9Ttw",
"topLevelComment": {
"snippet": {
"textOriginal": "This video is awesome!"
}
},
"videoId": "MILSirUni5E"
}
}
I tried like this and it didn't work:
$snippet->textOriginal('My comment');
How can I submit a featured comment using youtube API in php?