uploading attchment using web api c# or Vb.net

 Dim Req1 As New WindowsApplication1.ServiceReference1.SubmitMessageRequest
            Dim req As New WindowsApplication1.ServiceReference1.MessagingHubClient
        Dim payloadname As Object = "cid:IMP_DEC_Request_Draft.Xml"
        Dim attachment As Object = "F:\vs2015\WS1\WS1\IMP_DEC_Request_Draft.Xml"

        Req1.AttachmentFile = attachment
        Req1.DocumentType = "DEC_H2H_IN_REQ"
        Req1.Subject = "IMP_DEC_Request_Draft.Xml"
        Req1.PayloadName = payloadname

        Dim res = req.MessageSubmission(Req1)


        MessageBox.Show("Succeed")
    Catch ex As Exception
        MessageBox.Show(ex.Message)
    End Try