错误的签名尝试将curl中的文件上载转换为C＃

Question

I'm trying to upload a file with Keep2Share api

In the documentation are a Php Implementation, which are the following

$data = $this->getUploadFormData($parent_id, $preferred_node);
$curl = curl_init();
        $postFields = $data['form_data'];

        $postFields[$data['file_field']] = new CURLFile($file);

        curl_setopt_array($curl, [
            CURLOPT_FOLLOWLOCATION => false,
            CURLOPT_RETURNTRANSFER => true,
            CURLOPT_URL => $data['form_action'],
            CURLOPT_POST => true,
            CURLOPT_POSTFIELDS => $postFields,
        ]);

        $response = curl_exec($curl);
        if ($this->verbose) {
            echo '<<', $response, PHP_EOL;
        }
        return json_decode($response, true);

getUploadFormData method return a json with the following data

status: [success]
status_code: [200,400]
form_action: string
file_field: string
form_data: [
    params: string
    signature: string
]

But i need to translate it to C#, i'm trying the following

//dat is a object with getUploadForm data
var dat = await this.GetUploadFormData();

        HttpContent stringContent = new StringContent(dat.form_data.signature);
        HttpContent bytesContent = new ByteArrayContent(System.IO.File.ReadAllBytes(filename));

        using (var client = new HttpClient())

        using (var formData = new MultipartFormDataContent())
        {
            formData.Add(stringContent, "signature", "signature");
            formData.Add(bytesContent, "file", "file");
            var response = await client.PostAsync(dat.form_action, formData);

            using (var reader = new StreamReader(await response.Content.ReadAsStreamAsync()))
            {
                Console.WriteLine(await reader.ReadToEndAsync());
            }

            return await response.Content.ReadAsStreamAsync();
        }

But i'm getting

{"name":"Bad Request","message":"Wrong signature. IP 1**.58.*54.213","code":0,"status":400}

I'm almost sure that my problem is that I'm not passing the signature parameter as it should be

is that the case?

what i'm doing wrong?

Thanks!

EDIT

An example of getUploadFormData object should be

   "status":"success",
   "code":200,
   "form_action":"http://file-api-27.keep2share.cc:8000/upload",
   "file_field":"file",
   "form_data":{  
      "ajax":true,
      "_params":null,
      "signature":"2eda59a25137a78ef05513c60182cebe9972d9d1b80d9e643e0a8104dcdf42f59cfbc76680c7caf2d93e090c74ebdcf19da664c53e9da14992d604469a634887"
    }