Add line item product type to orders rest api output

add-line-item-product-type-rest-api.php

<?php
/**
 * Plugin Name: Line item product type in Orders REST API response.
 * Plugin URI:
 * Description: Display the product type in the line items array returned by WC REST API Orders requests.
 * Author: Prospress Inc, Matt Allan
 * Author URI: https://prospress.com/
 * Version: 1.0
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * @author Matt Allan
 * @since  1.0
 */

/**
 * Add product type to the order item meta in WC REST API output
 *
 * @param WP_REST_Response $response
 * @param WP_POST $post
 * @param WP_REST_REQUEST $request
 * @return WP_REST_Response $response
 */
function wcs_custom_add_product_type_api_order_item( $response, $post, $request ) {

	if ( ! empty( $response->data['line_items'] ) && function_exists( 'wc_get_product' ) ) {
		foreach( $response->data['line_items'] as $item_id => $line_item ) {
			if ( ! empty( $line_item['product_id'] ) ) {
				$product_id = ! empty( $line_item['variation_id'] ) ? $line_item['variation_id'] : $line_item['product_id'];
				$product    = wc_get_product( $product_id );

				$response->data['line_items'][ $item_id ]['product_type'] = $product->product_type;
			}
		}
	}

	return $response;
}
add_filter( 'woocommerce_rest_prepare_shop_order', 'wcs_custom_add_product_type_api_order_item', 10, 3 );
// add_filter( 'woocommerce_rest_prepare_shop_subscription', 'wcs_custom_add_product_type_api_order_item', 10, 3 );