问为什么两种(几乎)相似的上传文件到Slack的方法(使用c#)会导致不同的结果？

EN

public class PostMessage
    {       
        private string _token = "xoxp-MyToken";
        public string token { get { return _token; } }

        public string channel { get; set; }

        public string text { get; set; }

        public MultipartFormDataContent UploadFile()
        {
            var requestContent = new MultipartFormDataContent();
            var fileContent = new StreamContent(GetFile.ReadFile());
            requestContent.Add(new StringContent(token), "token");
            requestContent.Add(new StringContent(channel), "channels");
            requestContent.Add(fileContent, "file", Path.GetFileName(GetFile.path));

            return requestContent;
        }

    public static class GetFile
    {
        public static string path = @"C:\Users\f.held\Desktop\Held-Docs\Download.jpg";

        public static FileStream ReadFile()
        {            
            FileInfo fileInfo = new FileInfo(path);
            FileStream fs = new FileStream(path, FileMode.Open, FileAccess.ReadWrite);
            return fs;
        }
    }

    public class SlackClient
    {
        public Uri _method { get; set; }
        private readonly HttpClient _httpClient = new HttpClient {};

        public SlackClient(Uri webhookUrl)
        {
            _method = webhookUrl;
        }

        public async Task<HttpResponseMessage> UploadFileAsync(MultipartFormDataContent requestContent)
        {           
            var response = await _httpClient.PostAsync(_method, requestContent);

            return response;
        }
}

    public static void Main(string[] args)
            {
                Task.WaitAll(TalkToSlackAsync());                    

            private static async Task TalkToSlackAsync()
            {

                            var webhookUrl = new Uri("https://slack.com/api/files.upload");
                            var slackClient = new SlackClient(webhookUrl);

                            PostMessage PM = new PostMessage();
                            PM.channel = "DCW21NBHD";

                            var cont = PM.UploadFile();

                            var response = await slackClient.UploadFileAsync(cont);
                            string content = await response.Content.ReadAsStringAsync();
        }          
}

    public async Task<HttpResponseMessage> SendFileAsync(MultipartFormDataContent requestContent)
    {
        _httpClient.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", "xoxp-MyToken");
        var response = await _httpClient.PostAsync(UriMethod, requestContent);

        return response;
    }

public class Message
{
    public class GetFile // Just pass a path here as parameter!
    {
        public static string path = @"C:\Users\f.held\Desktop\Held-Docs\Download.jpg";

        public static FileStream ReadFile()
        {
            FileInfo fileInfo = new FileInfo(path);
            FileStream fs = new FileStream(path, FileMode.Open, FileAccess.ReadWrite);
            return fs;
        }
    }

public class JsonObject

    {
            [JsonProperty("file")]
            public string file { get; set; }
            [JsonProperty("channels")]
            public string channels { get; set; }
    }

class MainArea
{
    public static void Main( string[] args)
    {
        try
        {
            Task.WaitAll(SendMessage());
        }
        catch(Exception dudd)
        {
            Console.WriteLine(dudd);
            Console.ReadKey();
        }
    }
    private static async Task SendMessage()
    {
        var client = new BpsHttpClient("https://slack.com/api/files.upload");
        JsonObject JO = new JsonObject();
        JO.channels = "DCW21NBHD";

        var Json = JsonConvert.SerializeObject(JO, new JsonSerializerSettings { NullValueHandling = NullValueHandling.Ignore });

        var StringJson = new StringContent(Json, Encoding.UTF8, "multipart/form-data");
        var DeSon = JsonConvert.DeserializeObject(Json);

        Console.WriteLine(DeSon);
        Console.ReadKey();

        var requestContent = new MultipartFormDataContent();
        var fileContent = new StreamContent(Message.GetFile.ReadFile());
        requestContent.Add(fileContent, "file", Path.GetFileName(Message.GetFile.path));
        requestContent.Add(StringJson);

        var ResponseFile = await client.SendFileAsync(requestContent);

        Console.WriteLine(ResponseFile);
        Console.ReadKey();
    }
}

"shares":{"private":{"DCW21NBHD":[{"reply_users":[],"reply_users_count":0,"reply_count":0,"ts":"1544025773.001700"}]}},"channels":[],"groups":[],"ims":["DCW21NBHD"]}}

"shares":{},"channels":[],"groups":[],"ims":[]}}