HOW TO USE ADVANCED CUSTOM FIELDS TO CREATE USER GROUPS

finctions.php

// https://www.quickcleancode.com/how-to-use-advanced-custom-fields-to-create-user-groups/
add_action('publish_post', 'notifyauthor');
function notifyauthor() {

   $loop = new WP_Query(array('post_type' => 'groups', 'posts_per_page' => -1, 'order' => 'ASC'));
   while ($loop->have_posts()) : $loop->the_post();

      if(have_rows('members')):

         while (have_rows('members')) : the_row();

            $author = get_sub_field('member');
            $author_id = $author['ID']; $leader = get_field('group_leader');
            $leader_id = $leader['ID'];
            $temp = get_field('temp_group_leader');
            $temp_id = $temp['ID'];
            $current = get_current_user_id();

            if($author_id == $current) {
               $subject = 'Post Published: ' . $post->post_title . '';

               if(get_field('temp_group_leader') && get_field('temp_leader')) {
                  $message = 'Hi ' . get_the_author_meta('first_name', $temp_id) . ', Looks like ' . get_the_author_meta('first_name', $author_id) . ' ' . $author_last = get_the_author_meta('last_name', $author_id) . ' just published a new post: ' . get_permalink($post_id) . '.';
wp_mail(get_the_author_meta('user_email', $temp_id), $subject, $message);
               } else {
                  $message = 'Hi ' . get_the_author_meta('first_name', $leader_id) . ', Looks like ' . $author_name . ' ' . $author_last . ' just published a new post: ' . get_permalink($post_id) . '.';
wp_mail(get_the_author_meta('user_email', $leader_id), $subject, $message);
               }
            }

         endwhile;
      endif;
   endwhile;

   wp_reset_query();
}