Trying to notify author of post that their post went from “Pending” to “Pub….”

Hello. I’m trying to notify the author when their post goes from Pending to Published.

I’m first trying to notify all members, and then once that is working I will make the small change. But, when a post is Published, people are not being notified. Sigh.

If someone could help, I’m having a terrible time with this.

<?php
/*
Plugin Name: Notify blog authors
Plugin URI: https://www.1pixelout.net/code/notify-authors-wordpress-plugin/
Description: Notifies all blog authors when a new post is published.
Version: 1.0
Author: Martin Laine
Author URI: https://www.1pixelout.net
*/

/*  Copyright 2005  Martin Laine  (email : [email protected])

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/

function notify_users() {
	global $wpdb, $post_ID;

	$users = $wpdb->get_results( "SELECT ID FROM $wpdb->usermeta WHERE meta_key = 'wp_user_level' && meta_value > 0" );
	$post = $wpdb->get_row( "SELECT post_author, post_title FROM $wpdb->posts WHERE ID = " . $post_ID );
	$authordata = get_userdata( $post->post_author );

	$blogname = get_settings( "blogname" );
	$subject = "New or updated content by " . $authordata->user_nickname;

	$text = $authordata->user_nickname . " has posted new content or updated content on the website.";
	$text = $text . "\n\nNew or updated article: " . $post->post_title;
	$text = $text . "\n\nRead it here: " . get_permalink( $post_ID );

	foreach ($users as $user) {
		if($user->ID != $post->post_author) {
			$user_data = get_userdata( $user->ID );

			mail( $user_data->user_email,
				  $subject,
				  $text,
				  "From: " . $blogname . " <" . get_settings( "admin_email" ) . ">" );
		}
	}
}

add_action('publish_post', 'notify_users');
?>