Как установить миниатюру поста из фронтенда?

$post_id = wp_insert_post($new_post);
require_once( ABSPATH . 'wp-admin/includes/image.php' );
require_once( ABSPATH . 'wp-admin/includes/file.php' );
require_once( ABSPATH . 'wp-admin/includes/media.php' );
$meta_name_img = "ad_img";
$count = 0;
 
foreach ($_FILES["pictures"]["error"] as $key => $error) {
    if ($error == UPLOAD_ERR_OK) {
        $count++;
        $tmp_name = $_FILES["pictures"]["tmp_name"][$key];
        $name = basename($_FILES["pictures"]["name"][$key]);
        @copy($tmp_name, ABSPATH.'wp-content/uploads/'.$name);
        $ad_meta_img_new = "ad_img".$count;
        add_post_meta($post_id, $ad_meta_img_new, get_site_url().'/wp-content/uploads/'.$name); 
    }
}
        $attach_id_img = media_handle_upload('ad_img1', $post_id ); 
        set_post_thumbnail($post_id, $attach_id_img);

<?php the_post_thumbnail(); ?><?php echo get_post_meta($post->ID, 'ad_img1', true) ?>