Hello Lynxai,
In general the web server is configured to open index.php or index.html by default.
For exemple, with the url
http://cajon.dscloud.me/cops/libros/,
it's
http://cajon.dscloud.me/cops/libros/index.html which is open.
It seems that your NAS doesn't do that. In that case, the good url is:
http://cajon.dscloud.me/cops/libros/...?platform=wood