在使用微信支付退款功能的时候请求退款API报400，已经把apiclient_cert.p12 安装在本地，并且放在项目根目录下，可以通过根目录访问到。

报错信息

{
    "message":"Request failed with status code 400",
    "name":"Error",
    "stack":"Error: Request failed with status code 400
    at createError (/Users/tang/Documents/myProject/koala/koala-server/node_modules/_axios@0.19.2@axios/lib/core/createError.js:16:15)
    at settle (/Users/tang/Documents/myProject/koala/koala-server/node_modules/_axios@0.19.2@axios/lib/core/settle.js:17:12)
    at IncomingMessage.handleStreamEnd (/Users/tang/Documents/myProject/koala/koala-server/node_modules/_axios@0.19.2@axios/lib/adapters/http.js:236:11)
    at IncomingMessage.emit (events.js:327:22)
    at endReadableNT (_stream_readable.js:1220:12)
    at processTicksAndRejections (internal/process/task_queues.js:84:21)",
    "config":{
        "url":"https://api.mch.weixin.qq.com/secapi/pay/refund",
        "method":"post",
        "data":"<xml><appid></appid><mch_id></mch_id><nonce_str></nonce_str><transaction_id></transaction_id><out_refund_no></out_refund_no><total_fee></total_fee><refund_fee></refund_fee><refund_desc></refund_desc><notify_url></notify_url><cert_path></cert_path><sign></sign></xml>",
        "headers":{
            "Accept":"application/json, text/plain, */*",
            "Content-Type":"text/xml;charset=utf-8",
            "User-Agent":"axios/0.19.2",
            "Content-Length":545
        },
        "transformRequest":[
            null
        ],
        "transformResponse":[
            null
        ],
        "timeout":0,
        "xsrfCookieName":"XSRF-TOKEN",
        "xsrfHeaderName":"X-XSRF-TOKEN",
        "maxContentLength":-1
    }
}