first of all my english not good, sorry for mistakes, i will do my best.
I’m trying to create a website with c# and asp.net core 8. I should to post data to a remote api for upload my videos. (DoodStream API). When i try to post my data to the API using Postman or BurpSuite or simple html form its returning 200 success and my videos are viewing on dashboard. But when I try to upload my videos with asp.net httpClient I’m gettin Malformed multipart POST error or Http 500 Error. I’m trying to solve problem about a week but i couldn’t.

The upload function.

 public async Task<string> UploadDSAsync(string apiUrl, string apiKey, string filePath)
        {


            using (var request = new HttpRequestMessage(HttpMethod.Post, $"{apiUrl}?key={apiKey}"))
            {
                using (var form = new MultipartFormDataContent())
                {                  
                    var ua = "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/126.0.0.0 Safari/537.36";
                    request.Headers.Add("User-Agent", ua);
                    var file = new ByteArrayContent(await File.ReadAllBytesAsync(filePath));
                    file.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("video/mp4");
                    file.Headers.ContentDisposition = new System.Net.Http.Headers.ContentDispositionHeaderValue("form-data")
                    {
                        Name = "file",
                        FileName = Path.GetFileName(filePath)
                    };
                    form.Add(new StringContent(apiKey), name: "api_key");
                    form.Add(file, name: "file", Path.GetFileName(filePath));
                    
                    request.Content = form;
                    var response = _httpClient.Send(request);
                    response.EnsureSuccessStatusCode();
                    return await response.Content.ReadAsStringAsync();
                    
            }
        }
    }

     [HttpPost]
        [ValidateAntiForgeryToken]
        [DisableRequestSizeLimit]
        [Route("[controller]")] 
        [RequestFormLimits(ValueLengthLimit = int.MaxValue, MultipartBodyLengthLimit = int.MaxValue)]
        public async Task<IActionResult> Upload(IFormFile file)
    {
        var url = $"https://doodapi.com/api/upload/server?key={apiKey}";
        var res = await _doodStreamService.GetUploadServerAsync(url);
//res equals the url value, doostream provide us different urls for post videos.


        if (res == null)
        {
            return BadRequest(res);
        }

        if (file == null || file.Length == 0)
        {
            return BadRequest("Dosya seçilmedi.");
        }

        var filePath = Path.GetTempFileName().Replace(".tmp", ".mp4");
        using (var stream = System.IO.File.Create(filePath))
        {
            await file.CopyToAsync(stream);
        }

        var result = await _doodStreamService.UploadDSAsync(res, apiKey, filePath);

        // Geçici dosyayı silin
        System.IO.File.Delete(filePath);

        return Ok(result);
    }

I want to show you a successfully HTTP Post request.

POST /upload/01?key=mykey HTTP/1.1
Host: io274l.video-delivery.net
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:127.0) Gecko/20100101 Firefox/127.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8
Accept-Language: tr-TR,tr;q=0.8,en-US;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate, br
Content-Type: multipart/form-data; boundary=---------------------------329310205013466975143905415842
Content-Length: 2789881
Origin: http://127.0.0.1:5500
Referer: http://127.0.0.1:5500/
Upgrade-Insecure-Requests: 1
Sec-Fetch-Dest: document
Sec-Fetch-Mode: navigate
Sec-Fetch-Site: cross-site
Sec-Fetch-User: ?1
Priority: u=1
Te: trailers
Connection: keep-alive

-----------------------------329310205013466975143905415842
Content-Disposition: form-data; name="api_key"

182790a84ywqe32dp5y9ty
-----------------------------329310205013466975143905415842
Content-Disposition: form-data; name="file"; filename="aaa.mp4"
Content-Type: video/mp4

ftypmp42mp42isomavc1Ímoovxmvhdâ$â$X@Ätrakhtkhdâ$â$@8,edts$elst»(mdia,mdhdâ$â$]ÀÃØUÄ:hdlrvideVimeo Artax Video Handlerºminfvmhd$dinfdrefurl zstbl²stsd¢avc18HH
AVC Codingÿÿ9avcCd*ÿágd*¬Ùx'å  pã3@hé{,ýøøcolrnclxstts8é`cttsê»ÒÒÒÒÒÒÒ¤Òv»éÒÒÒÒÒÒÒ¤Òv»éÒÒÒÒÒÒÒ¤Ò»ÒÒÒÒÒÒÒv»éÒv»éÒv»éÒÒÒÒÒv»éÒ¤ÒÒÒÒÒÒÒ¤Ò»ÒÒÒÒÒÒÒ¤Òv»éÒÒÒÒÒÒÒv»éÒv»éÒv»éÒÒÒÒÒ¤Ò»ÒÒÒÒÒÒÒv»éÒv»éÒv»éÒÒÒÒÒ¤Òv»éÒÒÒÒÒÒÒ¤Ò¤é¤é¤é¤é¤é¤é¤é»é$stssIÙ!stscôstsz8õDE©Ç
3

MORE VİDEO BYTES
...
...

-----------------------------329310205013466975143905415842--

Its returning http 200 and json data about the uploaded video.

And this is my other request asp.net doing but its returning http 500 and fail.

POST /upload/01?key=myapikey HTTP/1.1
Host: yu1073k.video-delivery.net
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/126.0.0.0 Safari/537.36
traceparent: 00-612759c4039f28f75b3b845b2154898f-c618443035899a1d-00
Content-Type: multipart/form-data; boundary="a0cc5a75-c0d5-4328-8007-6abab10c2ee5"
Content-Length: 2789859
Connection: keep-alive

--a0cc5a75-c0d5-4328-8007-6abab10c2ee5
Content-Type: text/plain; charset=utf-8
Content-Disposition: form-data; name=api_key

182790a84ywqe32dp5y9ty
--a0cc5a75-c0d5-4328-8007-6abab10c2ee5
Content-Type: video/mp4
Content-Disposition: form-data; name=file; filename=tmputfimX.mp4

ftypmp42mp42isomavc1Ímoovxmvhdâ$â$X@Ätrakhtkhdâ$â$@8,edts$elst»(mdia,mdhdâ$â$]ÀÃØUÄ:hdlrvideVimeo Artax Video Handlerºminfvmhd$dinfdrefurl zstbl²stsd¢avc18HH
AVC Codingÿÿ9avcCd*ÿágd*¬Ùx'å  pã3@hé{,ýøøcolrnclxstts8é`cttsê»ÒÒÒÒÒÒÒ¤Òv»éÒÒÒÒÒÒÒ¤Òv»éÒÒÒÒÒÒÒ¤Ò»ÒÒÒÒÒÒÒv»éÒv»éÒv»éÒÒÒÒÒv»éÒ¤ÒÒÒÒÒÒÒ¤Ò»ÒÒÒÒÒÒÒ¤Òv»éÒÒÒÒÒÒÒv»éÒv»éÒv»éÒÒÒÒÒ¤Ò»ÒÒÒÒÒÒÒv»éÒv»éÒv»éÒÒÒÒÒ¤Òv»éÒÒÒÒÒÒÒ¤Ò¤é¤é¤é¤é¤é¤é¤é»é$stssIÙ!stscôstsz8õDE©Ç
3!À}â`>ö´À$ÏDò ßþ!KKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKK¿BMORE BYTES
...

--a0cc5a75-c0d5-4328-8007-6abab10c2ee5--

By the way, in the both http request the video bytes are correct, the problem is not about that.

Doodstream api local upload documentation

I tried multiple times with burpsuite and postman, its returning http 200.
I want to upload it via my UploadDSAsync function.