add_action( 'wcwl_after_add_user_to_waitlist', 'email_admin_to_notify_of_user_joining_waitlist', 10, 2 );
function email_admin_to_notify_of_user_joining_waitlist( $product_id, $user ) {
$admin_email = get_option( 'admin_email' );
$product = wc_get_product( $product_id );
if ( $product ) {
$subject = 'A user has just joined a waitlist!';
$message = $user->user_email . ' has just joined the waitlist for ' . $product->get_title();
wp_mail( $admin_email, $subject, $message );
}
}