Downloading files defined in start arguments with Inno Setup Script

Question

I'm trying to make a script that downloads a file. That works. But now I want to define, which file should be downloaded using the start arguments, but it seems to not accept the parameters.

Thats the code:

function NextButtonClick(CurPageID: Integer): Boolean;
begin
  if CurPageID = wpReady then begin
    DownloadPage.Clear;
    DownloadPage.Add('https://<my url>/folder/{param:version|latest-stable}/download.exe', 'download.exe', '');
    DownloadPage.Show;
    try
      try
        DownloadPage.Download;
        Result := True;
      except
        SuppressibleMsgBox(AddPeriod(GetExceptionMessage), mbCriticalError, MB_OK, IDOK);
        Result := False;
      end;
    finally
      DownloadPage.Hide;
            FileCopy('{tmp}\download.exe', '{src}', true);
    end;
  end else
    Result := True;
end;

In the [Files] section is all correct, the only problem is that it does not work with the parameters. Can anyone help me?