c# - 使用 .Net Framework 3.5 实现 USAEPAY 支付网关

Question

我已经编写了下面的代码，但我得到了未经授权的访问异常，尽管我使用了正确的 API 密钥和 PIN。除了 401 错误代码，我没有收到任何详细的异常。

        try
        {
            string baseUrl = "https://sandbox.usaepay.com/api/v2/";

            string sourceKey = "_4ShK4j3D100uXJb07aEw1krwO80VYpM";
            
            string pin = "123456";
            string seed = Guid.NewGuid().ToString();
            string key = string.Concat(sourceKey, seed, pin);
           var plainTextBytes = System.Text.Encoding.UTF8.GetBytes(key);
        string authenticationKeySystem.Convert.ToBase64String(plainTextBytes);
             

            Epay usaepay = new Epay();
            usaepay.command = "sale";
            usaepay.amount = 200;
            usaepay.creditcard.number = "4000700011112221";
            usaepay.creditcard.expiration = "0921";
            usaepay.creditcard.cvc = 999;
            usaepay.lineitems = new List<Epay.Lineitems>
        {
            new Lineitems
            { name = "Test40",
            cost = 40,
            qty = 2
            },
            new Lineitems
            { name = "Test60",
            cost = 60,
            qty = 2
            }
        };

            string serializeData = JsonConvert.SerializeObject(usaepay);

            WebClient client = new WebClient();
            client.BaseAddress = baseUrl;
            client.Headers.Add(HttpRequestHeader.ContentType, "application/json");
            client.Headers.Add(HttpRequestHeader.Authorization, "Basic " + authenticationKey);
            ServicePointManager.SecurityProtocol = (SecurityProtocolType)768 | (SecurityProtocolType)3072;
            var response = client.UploadString("transactions", serializeData);

            var result = JsonConvert.DeserializeObject(response);
        }
        catch(Exception ex)
        {

        } 

请在上面提出建议