Adding a gift card code to the WooCommerce POS receipt template

functions.php

<?php 

// this goes in your theme functions.php file

function my_custom_wc_rest_shop_order_object($response)
{
  if (function_exists('is_pos') && is_pos()) {
    $data = $response->get_data();
    if (is_array($data['line_items'])) : foreach ($data['line_items'] as &$line_item) :
      if ($code = wc_get_order_item_meta($line_item['id'], '_ywgc_gift_card_number')) {
        $line_item['meta_data'][] = new WC_Meta_Data(array(
          'id' => '',
          'key' => 'Gift Card',
          'value' => $code,
        ));
      }
    endforeach; endif;
    $response->set_data($data);
  }
  return $response;
}

add_filter('woocommerce_rest_prepare_shop_order_object', 'my_custom_wc_rest_shop_order_object');