You specify the main URL as the search engine can have trouble determining which 1 need to be the main URL.  The next tutorial will show you the way to allow Canonical URLs in Prestashop 1.5. Modules in PrestaShop have the capability to edit or lengthen hooks. This enables https://addons.prestashop.com/en/seo-natural-search-engine-optimization/31857-automatic-google-rich-snippets-json-ld-open-graph-seo.html