The Guidelines presented ended up a bit outdated (thanks to improvements designed to google and payapl sites), but support for this module is very good. Try it Yourself » The external fashion sheet is often prepared in almost any text editor. The file should not include any HTML code, and https://www.presta-addons-modules.com/en/opencart-seo-automatic-google-rich-snippets-json-ld-integration-opengraph-twitter-tags-schemaorg.html