微信调用云支付退款接口，会报错：TypeError: Cannot read property 'refund' of undefined，找不到原因

const cloud = require('wx-server-sdk')
cloud.init()
// 云函数入口函数
exports.main = async (event, context) => {
  const res = await cloud.CloudPay.refund({
    "out_refund_no":"6021500073819217020204482144", //商户退款单号
    "out_trade_no":"6021500073819217020204282144",//商户系统内部订单号
    "nonce_str":"5K8264ILTKCH16CQ2502SI8ZNMTM67VS", //随机字符串
    "sub_mch_id": "1587492071",
    "total_fee": 1,
    "refund_fee": 1
  })
  return res
}

在后台已经设置了退款API权限，已经授权。云函数版本2.0.3，开发工具也是最新版本1.03.2005140