add_action('rest_api_init', 'register_routes');
function register_routes()
{

    register_rest_route(
        'v1',
        'book/add',
        array(
            'methods' => \WP_REST_Server::CREATABLE,
            'callback' => 'callback_function_name',
            'permission_callback' => '__return_true',
            'args' => [
                'isbn' => [
                    'title' => __('Book ISBN'),
                    'validate' => ['required', 'min:5']
                ],
                'image' => [
                    'title' => __('screenshot'),
                    'validate' => ['file', 'mimes:jpg,png']
                ],
                'meta' => [
                    'title' => __('meta'),
                    'validate' => 'required|array|min:3'
                ],
                'author' => [
                    'title' => __('Author Book'),
                    'validate' => ['required', function ($attribute, $value, $fail) {
                        if (strlen($value) < 10) {
                            $fail("Show Error in closure-based Validation");
                        }
                    }]
                ]
            ]
        )
    );
}

apply_filters('wp_rest_api_validate_args_key', 'validate');

apply_filters('wp_rest_api_validate_locale', get_locale());

apply_filters('wp_rest_api_validate_lang_dir', dirname(__FILE__) . '/lang');

apply_filters('wp_rest_api_validate_pre', 
    null, 
    \WP_REST_Response $response, 
    \WP_REST_Request $request, 
    $handler
);