Custom Email when a Member change its level

added-member-custom-email.php

<?php
/**
 * Send an email to the admin when a user changes its level.
 * 
 * @param int $level_id The ID of the new level.
 * @param int $user_id The ID of the user.
 * 
 */
function custom_pmpro_after_change_membership_level( $level_id, $user_id ) {
	//Bail if level_id is 0
	if ( empty( $level_id ) ) {
		return;
	}
	$level = pmpro_getLevel( $level_id );
	$user = get_userdata( $user_id );
	$admin_email = get_option( 'admin_email' );
	$subject = "a user has changed its level";
	$body = "User " . $user->user_login . " has changed its level to " . $level->name;
	wp_mail( $admin_email, $subject, $body );
}

add_action( 'pmpro_after_change_membership_level', 'custom_pmpro_after_change_membership_level', 10, 2 );