php - Send Notification to all users that followed some author

I'm trying to send notifications for who followed some author when he published new post!

But it always sent to only one user not to all the followers!

So how can i send to all followers ids?

Thanks!

UPDATE

Now it working after change $user_id to $author

$followers = get_user_meta($author, '_pwuf_followers', true);

Good luck!

function to_followers_only_notify( $new_status, $old_status, $post ) {

    global $post;

    if ( 'publish' !== $new_status or 'publish' === $old_status )
        return;

        $user_id = get_current_user_id();
        $followers = get_user_meta($user_id, '_pwuf_followers', true);
        $followers = array_unique($followers);

        $post = get_post($post->ID);
        $author = $post->post_author;
        $author_name = get_the_author_meta( 'display_name', $author );

        $title = '<strong>'.$author_name.'</strong> ' . __('Published new post', 'dw-notifications'). ' <strong>'.$post->post_title.'</strong>';
        $link =  get_permalink($post->ID);
        $image = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), 'post');
        $notif = array('title'=>$title, 'link' => $link, 'image' => $image);

        if ( !empty( $followers ) && is_array( $followers ) ) {

            $follower_ids = array();
            foreach( $followers as $follower ) {
                if ( is_numeric( $follower ) ) {

                    if(!$post->post_author || $post->post_author == $follower) continue;


                    $follower_ids[] = $follower;

                }
            }
            dwnotif_add_notification($follower_ids, $notif);
        }

}
add_action( 'transition_post_status', 'to_followers_only_notify', 10, 3 );