If you didn't provide a full link, community support can't test out the link. But, in general, 403 can happen if the permissions for the folder and/or file are incorrect. Almost always, folders should have 0755 permissions (owner full permissions, everyone else read/enter only) and files should be 0644 (owner read/write, everyone else read only).
they did kind of include a link, just without the http on it. http://matematicasaprobadas.pcriot.com/
unless they meant a specific page that they did not include.
(but it basically has links and a video)
even a broken video link could have caused their problem.
but from what i can see it appears to work now.