Enable the download products to show in the WP REST API
<?php
/*
 * Plugin Name: Easy Digital Downloads - Enable downloads in WP REST API
 * Description: Enable the download products to show in the WP REST API
 * Author: Easy Digital Downloads
 * Author URI: https://easydigitaldownloads.com/
 * Version: 1.0
 */

 /**
 * Adds additional arguments into the post type registration for downloads.
 *
 * @param array $download_args The existing array of arguments.
 *
 * @return array
 */
function eddwp_add_rest_for_dls( $download_args ) {
	$download_args['show_in_rest'] = true;
	$download_args['rest_base'] = 'downloads';

	return $download_args;
}
add_filter( 'edd_download_post_type_args', 'eddwp_add_rest_for_dls', 10, 1 );
To implement this snippet on your site, create a brand new, empty WordPress plugin and paste the above code inside.