So I have a controller method that creates an excel package and sends the response back to the user to save/download. The problem that I am having is that the response is not prompting the Open/Save dialog from appearing. Is there something I am missing?
 [HttpPost]
 public ActionResult Export()
 {
  var excel = do stuff to create open XML package
  using (var memoryStream = new MemoryStream())
  {
     Response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
     Response.AddHeader("content-disposition", "attachment;  filename=" + Convert.ToString(fileName).Replace(" ", "_") + ".xlsx");
     excel.SaveAs(memoryStream);
     memoryStream.WriteTo(Response.OutputStream);
     Response.BinaryWrite(excel.GetAsByteArray());
     Response.Flush();
     Response.End();
    }
   return null
