<?php
$appId  = '{YOUR_APP_ID}';
$apiKey = '{YOUR_API_KEY}';
$params = [
    'app_id'        => $appId,
    'out_trade_no'  => '20240101123456',
    'out_refund_no' => 'REF20240101001',
    'refund_amount' => '100',
    'refund_reason' => urlencode('退款'),
];
ksort($params);
$signStr = urldecode(http_build_query($params)) . '&key=' . $apiKey;
$params['sign'] = strtoupper(md5($signStr));

$ch = curl_init('{BASE_URL}/v1/transactions/refund.html');
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($params));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$result = curl_exec($ch);
curl_close($ch);
$response = json_decode($result, true);
print_r($response);

import hashlib
import requests
from urllib.parse import quote

app_id = '{YOUR_APP_ID}'
api_key = '{YOUR_API_KEY}'
params = {
    'app_id': app_id,
    'out_trade_no': '20240101123456',
    'out_refund_no': 'REF20240101001',
    'refund_amount': '100',
    'refund_reason': quote('退款'),
}
sorted_keys = sorted(params.keys())
sign_str = '&'.join(f'{k}={params[k]}' for k in sorted_keys) + '&key=' + api_key
params['sign'] = hashlib.md5(sign_str.encode()).hexdigest().upper()

resp = requests.post('{BASE_URL}/v1/transactions/refund.html', data=params)
print(resp.json())

import java.io.*;
import java.net.*;
import java.security.MessageDigest;
import java.util.*;

public class Refund {
    public static void main(String[] args) throws Exception {
        String appId = "{YOUR_APP_ID}";
        String apiKey = "{YOUR_API_KEY}";
        Map<String, String> params = new TreeMap<>();
        params.put("app_id", appId);
        params.put("out_trade_no", "20240101123456");
        params.put("out_refund_no", "REF20240101001");
        params.put("refund_amount", "100");
        params.put("refund_reason", URLEncoder.encode("退款", "UTF-8"));
        StringBuilder sb = new StringBuilder();
        for (Map.Entry<String, String> e : params.entrySet())
            sb.append(e.getKey()).append("=").append(e.getValue()).append("&");
        sb.append("key=").append(apiKey);
        String sign = md5(sb.toString()).toUpperCase();
        params.put("sign", sign);
        String result = doPost("{BASE_URL}/v1/transactions/refund.html", params);
        System.out.println(result);
    }
    static String md5(String s) throws Exception {
        MessageDigest md = MessageDigest.getInstance("MD5");
        byte[] digest = md.digest(s.getBytes("UTF-8"));
        StringBuilder sb = new StringBuilder();
        for (byte b : digest) sb.append(String.format("%02x", b));
        return sb.toString();
    }
    static String doPost(String url, Map<String, String> params) throws Exception {
        StringBuilder body = new StringBuilder();
        for (Map.Entry<String, String> e : params.entrySet())
            body.append(URLEncoder.encode(e.getKey(), "UTF-8"))
                .append("=").append(URLEncoder.encode(e.getValue(), "UTF-8")).append("&");
        HttpURLConnection conn = (HttpURLConnection) new URL(url).openConnection();
        conn.setRequestMethod("POST");
        conn.setDoOutput(true);
        conn.getOutputStream().write(body.toString().getBytes("UTF-8"));
        BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream(), "UTF-8"));
        StringBuilder resp = new StringBuilder();
        String line; while ((line = br.readLine()) != null) resp.append(line);
        return resp.toString();
    }
}

const crypto = require('crypto');
const axios = require('axios');
const querystring = require('querystring');

const appId = '{YOUR_APP_ID}';
const apiKey = '{YOUR_API_KEY}';
const params = {
    app_id: appId,
    out_trade_no: '20240101123456',
    out_refund_no: 'REF20240101001',
    refund_amount: '100',
    refund_reason: encodeURIComponent('退款'),
};
const sortedKeys = Object.keys(params).sort();
const signStr = sortedKeys.map(k => `=`).join('&') + '&key=' + apiKey;
params.sign = crypto.createHash('md5').update(signStr).digest('hex').toUpperCase();

axios.post('{BASE_URL}/v1/transactions/refund.html', querystring.stringify(params))
    .then(res => console.log(res.data));

using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Security.Cryptography;
using System.Text;

var appId = "{YOUR_APP_ID}";
var apiKey = "{YOUR_API_KEY}";
var paramList = new List<KeyValuePair<string, string>> {
    new("app_id", appId),
    new("out_trade_no", "20240101123456"),
    new("out_refund_no", "REF20240101001"),
    new("refund_amount", "100"),
    new("refund_reason", Uri.EscapeDataString("退款")),
};
paramList.Sort((a, b) => string.Compare(a.Key, b.Key, StringComparison.Ordinal));
var signStr = string.Join("&", paramList.Select(p => $"{p.Key}={p.Value}")) + "&key=" + apiKey;
using var md5 = MD5.Create();
var sign = BitConverter.ToString(md5.ComputeHash(Encoding.UTF8.GetBytes(signStr))).Replace("-","").ToUpper();
paramList.Add(new("sign", sign));

using var client = new HttpClient();
var resp = await client.PostAsync("{BASE_URL}/v1/transactions/refund.html", new FormUrlEncodedContent(paramList));
Console.WriteLine(await resp.Content.ReadAsStringAsync());

package main

import (
    "crypto/md5"
    "fmt"
    "io"
    "net/http"
    "net/url"
    "sort"
    "strings"
)

func main() {
    appId := "{YOUR_APP_ID}"
    apiKey := "{YOUR_API_KEY}"
    params := url.Values{}
    params.Set("app_id", appId)
    params.Set("out_trade_no", "20240101123456")
    params.Set("out_refund_no", "REF20240101001")
    params.Set("refund_amount", "100")
    params.Set("refund_reason", url.QueryEscape("退款"))
    keys := make([]string, 0)
    for k := range params { keys = append(keys, k) }
    sort.Strings(keys)
    var parts []string
    for _, k := range keys { parts = append(parts, k+"="+params.Get(k)) }
    signStr := strings.Join(parts, "&") + "&key=" + apiKey
    sign := fmt.Sprintf("%X", md5.Sum([]byte(signStr)))
    params.Set("sign", sign)

    resp, _ := http.PostForm("{BASE_URL}/v1/transactions/refund.html", params)
    body, _ := io.ReadAll(resp.Body)
    fmt.Println(string(body))
}