procedure TForm1.Button1Click(Sender: TObject);
var
  Stream: TStringStream;
begin
  Stream := TStringStream.Create(AXMLDoc.XML.Text, TEncoding.UTF8);
  try
    HTTPString := IdHTTPClient.Post('http://' + FHost + ':' + IntToStr(FPort) + FHttpRoot, Stream);
  finally
    Stream.Free;
  end;
end;