You specify the main URL since the search engine can have trouble determining which one particular should be the principal URL.  The following tutorial will demonstrate how to permit Canonical URLs in Prestashop 1.5. Canonical URLs are employed to stop duplicate material and to indicate to search engines like https://captainbookmark.com/story19155953/how-much-you-need-to-expect-you-ll-pay-for-a-good-google-tag-manager-prestashop