Can not download .apk file from asp.net web api in https

Question

My Web API code as below,working in http mode but do not work in https mode .No error show,just give me a http 204 state code,can not download apk file anyway,my server is windows 2012.Thank you!

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Web.Http;

namespace DownloadFileFromWebApi.Controllers
{
  [RoutePrefix("download")]
  public class DownloadController : ApiController
  {
    [Route("get_demo_file")]
    public HttpResponseMessage GetFileFromWebApi()
    {
      try
      {
        var FilePath = System.Web.Hosting.HostingEnvironment.MapPath(@"~/download/app.apk");
        var stream = new FileStream(FilePath, FileMode.Open);
        HttpResponseMessage response = new HttpResponseMessage(HttpStatusCode.OK);
        response.Content = new StreamContent(stream);
        response.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
        response.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment") { 
        FileName="app.apk"
        };
        return response;
      }
      catch
      {
        return new HttpResponseMessage(HttpStatusCode.NoContent);
      }
    }
  }
}