Create .txt file dynamically and attach same into email

Question

I am trying to create a .txt file dynamically and also after creating it with some content I need to send the same in attachment of email. Email sending with attachment working for me but the attached file is empty.

I am trying below code to do the same -

 using (var ms = new System.IO.MemoryStream())
                {
                    using (var writer = new System.IO.StreamWriter(ms))
                    {
                        StringBuilder sb = new StringBuilder();
                        sb.Append("Filte start here");
                        sb.AppendFormat("<test>{0}</test>", test);
                        sb.Append("File end here");
                        writer.Write(sb.ToString());
                        writer.Flush();

                        System.Net.Mime.ContentType ct = new System.Net.Mime.ContentType(System.Net.Mime.MediaTypeNames.Text.Plain);
                        System.Net.Mail.Attachment attach = new System.Net.Mail.Attachment(ms, ct);
                        attach.ContentDisposition.FileName = "temp.txt";
                        mail.Attachments.Add(attach);
                        try
                        {
                            SendEmailUtility.SendMail(mail);
                        }
                        catch (SmtpException e)
                        {
                            Console.WriteLine(e.ToString());
                        }
            }
}

It is not the duplicate of Attach a file from MemoryStream to a MailMessage in C# post because I am also doing the same thing what is suggested there but in my case sending empty attachment. So definitively there is something which I am missing in my code base.

Please let me know what I am doing wrong here.

Any help would be appreciated!