WordPress Create REST API

/*related posts api*/

function related_posts_endpoint( $request_data ) {

    $post_id = $request_data['post_id'];

    $uposts = get_posts(
        array(
            'post_type' => 'post',
            'category__in'   => wp_get_post_categories($post_id),
            'posts_per_page' => 10,
            'post__not_in'   => array($post_id),
        )
    );

    return  $uposts;
}

add_action( 'rest_api_init', function () {

    register_rest_route( 'custompostapi/v1', '/post/related/(?P<post_id>[\d]+)', array(
            'methods' => 'GET',
            'callback' => 'related_posts_endpoint'
    ));

});

Now, This is a WordPress REST API URL: https://readymadecode.com/wp-json/customrestapi/v1/post/related/254