Custom fields order (wordpress)

Order by first and last name from custom fields.

<?php
    $q = new WP_Query(array(
        'category_name' => 'orders',
        'meta_query' => array(
            'ln' => array(
                'key' => 'ln',
            ),
            'fn' => array(
                'key' => 'fn',
            ),
        ),
        'orderby' => array(
           'ln' => 'ASC',
           'fn' => 'ASC',
        ),
        'posts_per_page' => -1,
    ));
    if ($q->have_posts()) {
        echo '<ul>';
        while ($q->have_posts()) {
            $q->the_post();
            $fn = get_post_meta(get_the_ID(), 'fn', true);
            $ln = get_post_meta(get_the_ID(), 'ln', true);
            printf(
                '<li><a href="%s">FN: %s LN: %s</a></li>',
                esc_url(get_permalink()),
                $fn,
                $ln
            );
        }
        echo '</ul>';
        wp_reset_postdata();
    }
?>

template.php

< toolbox