Demo Product html linking

[Xplicit Halostar]

I'm wondering why I cannot do a specific, clickable, html/hypertext-able direct link to a product that I've purchased full perm, so that people can try the demo & would be able to click the link to go to that page, rather than having to copy & paste the link into a new webpage?. I get this not allowed error when I try to update the MP listing....is there no way to add a clickable link? Or am I using the incorrect format? I was trying to use this:  <a href=" https://marketplace.secondlife.com/p/racerbacktankDEMO/14907199  "></a> (left spaces between "  " marks intentionally in here. It would be nice if I can do that, as it stands it only lets me put a copy/pasting link in my MP listing(s).