Set Advert image to featured image automatically

Hi,

Great, great plugin. And also, thanks for the great documentation. I had some trouble setting the Advert image to featured post image so that I can grid the Adverts using Visual Composer on some pages. I came up with the following code;

// Custom Function: Get Attachment ID from URL

function p_get_image_id($image_url) {
	global $wpdb;
	$attachment = $wpdb->get_col($wpdb->prepare("SELECT ID FROM $wpdb->posts WHERE guid='%s';", $image_url ));
        return $attachment[0];
}

// Custom Function: Add Auto Featured Image

function auto_featured_image() {
    global $post;

    if (!has_post_thumbnail($post->ID)) {
        $attached_image = get_children( "post_parent=$post->ID&post_type=attachment&post_mime_type=image&numberposts=1" );

      if ($attached_image) {
              foreach ($attached_image as $attachment_id => $attachment) {
                   set_post_thumbnail($post->ID, $attachment_id);
              }

         } else {
            if ( get_post_type($post->ID) == 'advert' ) {
            $image_url = "https://www.sinavlar.net/media/2016/11/classified-ni.jpg";
            $attachment_id = p_get_image_id( $image_url );
                  set_post_thumbnail($post->ID, $attachment_id);
            } else if ( get_post_type($post->ID) == 'post' ) {
            $image_url = "https://www.sinavlar.net/media/2016/11/sinavlarnet-haber.jpg";
            $attachment_id = p_get_image_id( $image_url );
                  set_post_thumbnail($post->ID, $attachment_id);
            }
         } 
    }
}
// This was used to generate all featured images for old posts
// add_action('the_post', 'auto_featured_image');
// Used for new posts
add_action('save_post', 'auto_featured_image');
add_action('draft_to_publish', 'auto_featured_image');
add_action('new_to_publish', 'auto_featured_image');
add_action('pending_to_publish', 'auto_featured_image');
add_action('future_to_publish', 'auto_featured_image');

This works well when creating Adverts from the admin panel. However, I ran into problems when I tried to use the front-end posting form. Could you lend me a hand with this, thanks!