Ordering with WP REST API

wp-rest-api-order-by.php

<?php

add_filter('rest_post_query', [$this, 'sortByDate'], 10, 2);

public function sortByDate($args, $request)
{
    if ($args['post_type'] !== 'event') {
        return $args;
    }

    $now = time();
    $order = [
        'meta_key' => 'start_date',
        'orderby' => 'meta_value_num',
        'order' => 'ASC',
        'meta_query' => [
            [
                'key' => 'end_date',
                'value' => ($now - ($now % 86400)),
                'type' => 'DECIMAL',
                'compare' => '>=',
            ]
        ]
    ];

    return array_merge($args, $order);
}