Facebook has defined a range of catalog fields that its algorithm uses to optimize the experience of buyers when using Facebook shop and checkout and also improves ad performance.
Options
Use product options as catalog fields in the product feed.
We list options that actually exist in any of the products that are included in the feed.
When the feed is generated, we - for every product in the feed - look up all product options.
Then we present these (all options of all products) in the app admin. Users can map each option to a Facebook product catalog field.
Metafields
Use any product or variant metafield to add catalog fields to the product feed.
The metafield key will be the catalog field name in the feed and the value will be the catalog field value.
Tags
Use the Shopify tags in the form 'color:red', 'gender-male' or 'age_group=female' to add catalog fields to the product feed.
In the feed will appear:
metafields['flexify']['farbe']='green' ➡️ <g:color><![CDATA[ green ]]></g:color>
product.tags="farbe=green" ➡️ <g:color><![CDATA[ green ]]></g:color>