Magento 2 Rest API：无法下订单。出错

Question

致命错误：未捕获的GuzzleHttp \ Exception \ ClientException：客户端错误：PUT http://magento.localhost.com/rest/V1/carts/4/order导致400 Bad Request响应：{“ message”：“请指定一种运送方式。”}

我的代码：

$shipBill = '{
 "addressInformation": {
  "shipping_address": {
   "id": 60,
   "customer_id": 1,
   "region": "Arkansas",
   "region_id": 5,
   "country_id": "US",
   "street": [
    "Whitefield,New York"
   ],
   "company": "IBM",
   "telephone": "94354545",
   "postcode": "234533",
   "city": "New York",
   "firstname": "test",
   "lastname": "test",
   "prefix": "address_",
   "region_code": "AR"
  },
  "billing_address": {
   "id": 60,
   "customer_id": 1,
   "region": "Arkansas",
   "region_id": 5,
   "country_id": "US",
   "street": ["Whitefield,New York"],
   "company": "IBM",
   "telephone": "94354545",
   "postcode": "234533",
   "city": "New York",
   "firstname": "test",
   "lastname": "test",
   "prefix": "address_",
   "region_code": "AR"
  },
  "shipping_method_code": "flatrate",
  "shipping_carrier_code": "flatrate"
     }
      }';
$checkout = $magento->createShippingAndBilling($quoteId, $shipBill)->getInArray();

$payment = '
    {
    "paymentMethod": {
        "method": "checkmo"
    }
}';
$order = $magento->orderCreate($quoteId, $payment)->getInArray();

我已通过其余API在购物车中添加了商品。只有当我尝试下订单时，一切都正常了。