Why this comes before ads

Every ad dollar is either informed by data or spent on guessing. Conversion tracking tells the algorithm what a buyer looks like so it can find more of them.

Without it:

Meta shows your ads to people who scroll but never buy
Google optimizes for clicks, not sales
You can't measure what a customer costs you or whether ads pay back
Budget decisions come from feelings

Set up tracking and verify it with a real order before you spend a dollar on ads.

Browser, server, and native

There are three ways an event reaches Meta or Google:

Browser tag: a script on your site (the Meta pixel, the Google tag). It sees page views, clicks, and campaign context, but ad blockers, iOS privacy, and cookie choices can lose events.
Server event: your server sends the event directly (Meta Conversions API, GA4 Measurement Protocol). It's reliable for confirmed facts like a paid order, but it only knows what you pass into it.
Native integration: the platform's own connection, like Shopify's Meta and Google channels. It's closest to the checkout and maintained for you.

Server-side isn't automatically better. It's better for confirmed payments and worse for knowing what someone looked at. Most stores need both, deduplicated.

The setup for a product business

Use the native integrations first. Connect Shopify's Meta channel and Google channel. They handle the standard purchase events.
Turn on the Meta Conversions API through the integration so purchases still arrive when the browser pixel gets blocked.
Connect GA4 and confirm purchases show up with the right order value.
Don't add a second copy. Adding your own pixel code next to Shopify's integration double-counts. Shopify warns about this.
Test with a real order on a phone and confirm it arrives once in each platform.

Everything else, like custom events, server webhooks, and headless storefronts, is covered in the analytics deep dive.

How the platforms use this data

Meta uses your purchase data to decide who sees your ads. Clean data means the algorithm learns who buys. Broken data means it learns who clicks.

Google Ads bids toward the conversions you tell it matter. Import one primary purchase conversion, not three.

Amazon is a walled garden. Your conversion data comes from Amazon's own reports (sessions, conversion rate, search terms), not from your pixel.