These scripts send event and customer data to the Google Tag Manager data layer. With the help of these two scripts, you can set up a Facebook conversion API for Shopify for these events: pageview, add to cart, view content, and purchase. It should work together with the native Facebook app for Shopify with enabled maximum tracking.
analytics.js sends product data and Facebook event ID (generated by the Facebook app for Shopify) to the data layer of the Google Tag manager Web container.
analytics.liquid sends user data to the data layer. You can use customer data to increase the event match quality score for Facebook conversion API.
Follow this guide on setting up FB CAPI for Shopify.
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