## 下载账单
```bash
import WxPay from 'wechatpay-node-v3';
import fs from 'fs';

const pay = new WxPay({
  appid: '直连商户申请的公众号或移动应用appid',
  mchid: '商户号',
  publicKey: fs.readFileSync('./apiclient_cert.pem'), // 公钥
  privateKey: fs.readFileSync('./apiclient_key.pem'), // 秘钥
});
```
## 使用
```bash
const data = await pay.downloadbill(download_url);
```