You specify the primary URL since the online search engine may have issues figuring out which a single need to be the main URL.  The next tutorial will tell you about how you can enable Canonical URLs in Prestashop 1.5. By default, PrestaShop's deep URLs (which is, distinct pages https://bookmarkblast.com/story19246297/the-2-minute-rule-for-automatische-hreflang-tags-und-kanonische-tags-seo