You specify the primary URL because the online search engine might have problem figuring out which a person need to be the main URL.  The next tutorial will tell you about how you can permit Canonical URLs in Prestashop 1.5. Improve the indexing of the Prestashop urls in Google. https://addons.prestashop.com/fr/seo-referencement-naturel/31857-seo-automatique-google-rich-snippets-json-ld-open-graph.html