FileData is empty while uploading multipart media file

Question

I'm using Postman and my own Restsharp based client to send the audio file to the web API controller when size exceeded from 3 or 4 MB provider.FileData showing contains 0 files.

I also tried to use this but can't be solved the problem. var provider = new MultipartFileStreamProvider(root);

    public async Task<HttpResponseMessage> UploadFile()
    {
        HttpRequestMessage request = this.Request;
        if (!request.Content.IsMimeMultipartContent())
        {
            throw new HttpResponseException(HttpStatusCode.UnsupportedMediaType);
        }

        string root = System.Web.HttpContext.Current.Server.MapPath("~/App_Data/uploads");
        var provider = new MultipartFormDataStreamProvider(root);

        var task = await request.Content.ReadAsMultipartAsync(provider).
            ContinueWith<HttpResponseMessage>(o =>
                {
                    FileInfo finfo = new FileInfo(provider.FileData.First().LocalFileName);
                    string guid = Guid.NewGuid().ToString();
                    string fileName = guid + "_" + provider.FileData.First().Headers.ContentDisposition.FileName
                                          .Replace("\"", "");
                    File.Move(finfo.FullName, Path.Combine(root, fileName));

                    return new HttpResponseMessage()
                    {
                        Content = new StringContent("File uploaded.")
                    };
                }
            );

        return task;
    }