You specify the main URL since the online search engine may have issues figuring out which one particular should be the principal URL.  The next tutorial will teach you how to allow Canonical URLs in Prestashop 1.five. It can even enable you to add the default "x-default" tag for https://addons.prestashop.com/ru/seo-natural-search-engine-optimization/31857--rich-snippets-json-ld-opengraph-seo.html