使用C#代码，微信公众号推送图片 报错为”errmsg”:”mediadata missing hint:

我的代码是这样写的(https://i.stack.imgur.com/mU6At.jpg)
public async Task UploadMediaAsync(string accessToken, string filePath, string mediaType)
{
Debug.WriteLine($”Preparing to upload file. Access token: {accessToken}, File path: {filePath}, Media type: {mediaType}”);

    if (!File.Exists(filePath))
    {
        throw new FileNotFoundException("File not found.", filePath);
    }

    var fileInfo = new FileInfo(filePath);
    var fileName = fileInfo.Name;
    var contentType = MimeMappingHelper.GetMimeMapping(fileName);
    var fileLength = fileInfo.Length;

    string uploadUrl = $"https://api.weixin.qq.com/cgi-bin/media/upload?access_token={accessToken}&type={mediaType}";

    using (var fileStream = File.OpenRead(filePath))
    {
        var fileContent = new StreamContent(fileStream);
        fileContent.Headers.ContentDisposition = new ContentDispositionHeaderValue("form-data")
        {
            Name = ""media"",
            FileName = $""{fileName}""
        };
        fileContent.Headers.ContentType = new MediaTypeHeaderValue(contentType);

        var formData = new MultipartFormDataContent
    {
        { fileContent, "media", fileName }
    };

        Debug.WriteLine("Sending the request to upload file...");
        var response = await _httpClient.PostAsync(uploadUrl, formData);
        var responseContent = await response.Content.ReadAsStringAsync();
        Debug.WriteLine($"Upload response: {responseContent}");

        if (!response.IsSuccessStatusCode)
        {
            throw new HttpRequestException($"Request failed with status code: {response.StatusCode}, Content: {responseContent}");
        }

        var uploadData = JsonConvert.DeserializeObject<dynamic>(responseContent);
        if (uploadData.errcode != null)
        {
            throw new Exception($"Error in upload response: {responseContent}");
        }

        Debug.WriteLine($"Media ID: {uploadData.media_id}");
        return uploadData.media_id;
    }
}