There are two requirements to get Snapchat Dynamic Ads up and running: their tracking pixel and a product catalog.
The pixel is the tracking mechanism on a website that feeds behavior and visit information back to Snapchat so it recognizes when those users are later on the platforms. These events must match to at least 1,000 Snapchat users in order to activate dynamic ads.
The common thread that lets Snap know what product to show is passed via the item_id parameter. This must be present and fed back to Snapchat for Page Views, View Content, Add to Cart, and Purchase actions.
The item_id parameter is then matched to the product catalog a brand uploads so the ad unit will pull the correct photo and pricing.