10
sorry, what I would mean is
• open your mainfile.php
• copy XOOPS_ROOT_PATH, eg for a local site : c:/wamp/www/my-shop
• open product form and paste it into field "Path of the file to download"
• correct path by adding folder(s) and file name (eg : c:/wamp/www/my-shop/uploads/downloads/myfile.php)
... be careful : for a production website, all " / " are " \ "