Hi,
It's probably because the URL
yourwebsite.com/panthera-liner
is not a valid URL. And thus the Joomla router redirects that URL to the 301 joomla article which is set to display when the URL used is invalid.
In the canonical URL field, you can't put any URL. You can only put there one of the URLs of the product page.
So for example, instead of /inchiostri-tattoo/panthera/product/panthera-liner you could put /inchiostri-tattoo/panthera/product/XXX-panthera-liner where XXX is the id of the product or /component/hikashop/product/show/cid-XXX , etc.