How to set the “main” photo in a blogger when creating (api) an article?

Question

Google

Good afternoon!
Recently I began to study the Google API/API Blogger, I have already learned how to create posts in it, but I just can’t figure out how to take a photo that will then end up on a thumbnail for an article. When I manually upload a photo to an article through the blogger editor, it is automatically marked, and when the article is saved, it becomes a thumbnail. I even tried to take the HTML code from the editor and use it when working with the API, but this only affected the content, but the photo, as the main one, is not marked.

Here is part of the code:

$service = new Google_Service_Blogger( $client );
$html = array();
$html[] = '
<div class="separator" style="clear: both; text-align: center;">
  <a href="https://'.$img.'" imageanchor="1" style="margin-left: 1em; margin-right: 1em;">
    <img border="0" src="https://'.$img.'" />
  </a>
</div>';
$html[] = '<p>Content</p>';
$html = implode( '', $html );

$image = new Google_Service_Blogger_PostImages();
$image->setUrl( 'https://'.$img );

$data = new Google_Service_Blogger_Post();
$data->setTitle( 'Test' );
$data->setContent( $html );
$data->setLabels( $labels );

$data->setImages( array( $image ) );

$res = $service->posts->insert( $blogID, $data, array(
  'isDraft' => true,
  'fetchImages' => true,
) );
echo '<pre>'.print_r( $res, true ).'</pre>';

I used this code for the test, I didn’t even really understand what it should do, but it still doesn’t work:
$data->setImages( array( $image ) );