SagePay API - 创建事务时请求格式不正确

Question

我可能在这里遗漏了一些非常简单的东西...我正在尝试根据docs创建一个新的交易，SagePay说请求格式不正确，但我看不出有什么问题是

我的请求有效负载如下所示：

{
  "transactionType": "Payment",
  "paymentMethod": {
    "card": {
      "merchantSessionKey": "912164F4-XXXX-XXXX-XXXX-BFA64856C7A8",
      "cardIdentifier": "78A8232B-XXXX-XXXX-XXXX-90EC65622666"
    }
  },
  "entryMethod": "Ecommerce",
  "vendorTxCode": "1234556",
  "description": "Online payment script.",
  "amount": 99,
  "currency": "GBP",
  "customerFirstName": "Bob",
  "customerLastName": "Smith",
  "customerPhone": "07911883621",
  "billingAddress": {
    "address1": "20 XXXXXX",
    "address2": "XXXXX",
    "city": "XXXXX",
    "postalCode": "XXX XXX",
    "country": "GB",
    "state": ""
  }
}

SayPay的回复如下：

{
  "code": 1000,
  "description": "Incorrect request format"
}

我做错了什么？