抖音开放平台的上传视频到文件服务器（/video/upload/）API为什么总是返参数不合法回？

API文档地址：
https://open.douyin.com/platform/doc/OpenAPI-video-create

调用接口：

接口参数：

平台已申请的权限：

问题描述：

在调用 https://open.douyin.com/video/upload/接口是总数返回参数不合法，用该接口调用时所使用的open_id和access_token调用其他接口（如：/video/list/）都可返回调用成功数据，可以肯定的是，open_id和access_token参数没有问题，接口权限 （Scope: “video.create”）在开放平台已经申请并审核通过，在扫码授权时，也已经传如了Scope权限。

调用API返回结果如下：

{"data":{"description":"参数不合法","error_code":2100005},"extra":{"logid":"202003211443340100140470891DF1B821","now":1584773018222}}

注：接口测试采用多种测试方式都是这个结果：

所采用的测试方式有：

1）C# 程序调用

2）jquery前端直接调用

3) postman调用

C# 实现代码：

var userInfo = _sessionHelper.GetSession();
                var url = "https://open.douyin.com/video/upload";
                string filePath = @"D:/dy3.mp4";

                Dictionary<string, string> dicData = new Dictionary<string, string>();
                dicData.Add("open_id", userInfo.data.open_id);
                dicData.Add("access_token", userInfo.data.access_token);

                Dictionary<string, string> dicFiles = new Dictionary<string, string>();
                dicFiles.Add("video", "D:/dy3.mp4");
                var res = Util.PostHttpResponse(url, dicData, dicFiles);

PostHttpResponse方法：

public static string PostHttpResponse(string url, Dictionary<string, string> postData, Dictionary<string, string> files)
        {
            HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
            CookieContainer cookieContainer = new CookieContainer();
            request.CookieContainer = cookieContainer;
            request.AllowAutoRedirect = true;
            request.Method = "POST";
            string boundary = DateTime.Now.Ticks.ToString("X"); // 随机分隔线
            request.ContentType = "multipart/form-data;charset=utf-8;boundary=" + boundary;

            byte[] itemBoundaryBytes = Encoding.UTF8.GetBytes("\r\n--" + boundary + "\r\n");
            byte[] endBoundaryBytes = Encoding.UTF8.GetBytes("\r\n--" + boundary + "--\r\n");

            Stream postStream = request.GetRequestStream();
            postStream.Write(itemBoundaryBytes, 0, itemBoundaryBytes.Length);

            //写入文本
            if (postData != null && postData.Count > 0)
            {
                var keys = postData.Keys;
                foreach (var key in keys)
                {
                    string strHeader = string.Format("Content-Disposition: form-data; name=\"{0}\"\r\n\r\n", key);
                    byte[] strByte = System.Text.Encoding.UTF8.GetBytes(strHeader);
                    postStream.Write(strByte, 0, strByte.Length);

                    byte[] value = System.Text.Encoding.UTF8.GetBytes(string.Format("{0}", postData[key]));
                    postStream.Write(value, 0, value.Length);

                    postStream.Write(itemBoundaryBytes, 0, itemBoundaryBytes.Length);

                }
            }
            postStream.Write(itemBoundaryBytes, 0, itemBoundaryBytes.Length);

            //写入文件
            if (files != null && files.Count > 0)
            {
                var keys = files.Keys;

                foreach (var key in keys)
                {
                    string filePath = files[key];
                    int pos = filePath.LastIndexOf("\\");
                    string fileName = filePath.Substring(pos + 1);
                    StringBuilder sbHeader = new StringBuilder(string.Format("Content-Disposition:form-data;name=\"{0}\";filename=\"{1}\"\r\nContent-Type:application/octet-stream\r\n\r\n", key, fileName));
                    byte[] postHeaderBytes = Encoding.UTF8.GetBytes(sbHeader.ToString());

                    FileStream fs = new FileStream(files[key], FileMode.Open, FileAccess.Read);
                    byte[] bArr = new byte[fs.Length];
                    fs.Read(bArr, 0, bArr.Length);
                    fs.Close();
                    postStream.Write(postHeaderBytes, 0, postHeaderBytes.Length);
                    postStream.Write(bArr, 0, bArr.Length);

                    postStream.Write(itemBoundaryBytes, 0, itemBoundaryBytes.Length);
                }

            }
            postStream.Write(endBoundaryBytes, 0, endBoundaryBytes.Length); //结束标志
            postStream.Close();
            //发送请求并获取相应回应数据
            HttpWebResponse response = request.GetResponse() as HttpWebResponse;
            //直到request.GetResponse()程序才开始向目标网页发送Post请求
            Stream instream = response.GetResponseStream();
            StreamReader sr = new StreamReader(instream, Encoding.UTF8);
            //返回结果网页（html）代码
            string content = sr.ReadToEnd();
            return content;
        }

这里要求你使用 multipart/form-data 传 json
你是不是不是multipart/form-data，也就是类似 base64 那种带有分段的，以及传入的内容不是json
检查下