How Conversion APIs Work: Meta CAPI and Google Enhanced Conversions Explained

What Are Conversion APIs?

Conversion APIs (sometimes called CAPIs) are server-side integrations that let you send conversion data directly from your server to an ad platform. Instead of relying on a browser pixel to fire when a user lands on a thank-you page, a Conversion API sends the event from your backend, bypassing the browser entirely.

Meta, Google, and TikTok each offer their own version. The mechanics differ slightly, but the core idea is the same: your server tells the ad platform that a conversion happened, along with whatever user-matching data you have, so the platform can attribute it to the right ad and use it for bid optimisation.

This is a separate concept from server-side tracking in the affiliate sense. Both are server-to-server, but they solve different problems for different audiences. More on that distinction below.

Why Conversion APIs Exist

Browser pixels were the standard for over a decade, but they've become increasingly unreliable. Ad blockers, iOS Intelligent Tracking Prevention, the deprecation of third-party cookies, and page load failures all chip away at the signal that ad platforms receive. The result is why ad platform data is often inaccurate even when your actual revenue is healthy.

When an ad platform can't see your conversions, its algorithm optimises on incomplete signals. You end up paying more for traffic that converts less, because the platform is flying blind on what's actually working. Conversion APIs restore that signal by routing it through a channel the browser can't interfere with.

The rise of Conversion APIs is part of a broader shift toward the future of advertising measurement, where first-party data and direct server integrations replace browser-dependent tracking.

Meta Conversions API (CAPI)

Meta's Conversions API is the most widely adopted of the three. It allows you to send web events (purchases, leads, add-to-carts) and app events from your server directly to Meta's Graph API. Meta uses these events to power its ad delivery algorithm and attribution reporting.

The CAPI is designed to work alongside the Meta Pixel, not necessarily replace it. When both are active, Meta uses an event_id parameter to deduplicate events that arrive through both channels. Without deduplication configured correctly, you'll report inflated conversion numbers and the algorithm will receive a distorted signal.

User matching is central to how Meta CAPI works. To attribute a server-side event to the correct user, you need to send hashed first-party data alongside the event. The accepted parameters include:

• Email address (SHA-256 hashed)
• Phone number (SHA-256 hashed, E.164 format)
• IP address and user agent
• Client-side fbp and fbc cookies when available
• External ID (your own customer identifier, hashed)

More matching parameters improve your event match quality score. A higher match quality means more conversions are attributed, which feeds the algorithm better data. Events sent with only an IP address will match far fewer users than events enriched with hashed email and phone.

Google Enhanced Conversions

Google's equivalent is called Enhanced Conversions. Rather than replacing your existing Google Ads conversion tag, Enhanced Conversions supplements it by sending hashed first-party data from your server that Google uses to improve match rates.

The mechanism works like this: when a user converts, you capture their email address or phone number (typically from a form submission or checkout), hash it with SHA-256, and send it to Google alongside the standard conversion event. Google attempts to match the hashed data to a signed-in Google account, improving attribution across devices and in environments where cookies are blocked.

Enhanced Conversions is particularly valuable for logged-in Google users converting on iOS or in cookieless environments. It partially restores the attribution signal that iOS privacy changes eroded. Google reports that advertisers using Enhanced Conversions typically see measurable improvements in reported conversion volume, as previously unattributed conversions get matched.

Unlike Meta CAPI, Google Enhanced Conversions does not require you to send the event independently. It works as an enrichment layer on top of your existing Google tag infrastructure, which makes implementation somewhat simpler if your Google Ads setup is already solid.

TikTok Events API

TikTok's Events API is the server-side equivalent of the TikTok Pixel. It supports both web and app events, and like Meta CAPI, it's designed to complement the client-side pixel rather than fully replace it.

The Events API accepts standard e-commerce events: Purchase, AddToCart, InitiateCheckout, CompleteRegistration, and custom events you define. You send these events to TikTok's server API endpoint along with user properties (hashed email, phone, IP, user agent) for matching.

TikTok also uses an event_id field for deduplication when both pixel and Events API are active. As with Meta, deduplication needs to be correctly configured to avoid double-counting. TikTok's algorithm is less mature than Meta's, but CAPI signal quality still affects delivery and optimisation, especially as TikTok ads scale.

S2S Affiliate Tracking vs Conversion APIs: Key Differences

These two technologies are both "server-side" and both involve sending conversion data, but they serve completely different purposes. Conflating them causes real confusion for media buyers managing both affiliate and paid social campaigns.

S2S tracking in the affiliate context is about attribution between your tracker and affiliate networks. When a conversion fires, the affiliate network sends a postback to your tracker with the click ID. Your tracker records the payout and attributes it to the correct campaign, creative, and traffic source. This is how you know which of your campaigns is profitable.

Conversion APIs, by contrast, are about sending conversion signals to ad platforms so their algorithms can optimise delivery. Meta doesn't care about your affiliate network postbacks. It cares whether a purchase event arrived with enough user-matching data to attribute to one of its ads and feed its bidding model.

The practical difference:

• S2S tracking tells your tracker which clicks converted. It answers the question: which campaigns, placements, and creatives are profitable?
• Conversion APIs tell the ad platform which users converted. They answer the question: how does the platform's algorithm improve bidding and targeting based on your conversion data?

Both should be running simultaneously. Your S2S postback feeds your tracker for internal reporting and optimisation. Your CAPI integration feeds the ad platform for algorithmic optimisation. They operate in parallel and serve different recipients.

How to Implement Conversion APIs

Each platform has its own API, but the implementation requirements follow a similar pattern across all three.

• Server infrastructure. You need a server (or serverless function) that can receive conversion events from your application and forward them to the ad platform's API endpoint. This is typically triggered at the point of conversion, such as a successful payment or form submission on your backend.
• Event deduplication logic. If you're running both a browser pixel and a CAPI integration, every event must carry a consistent event_id. The pixel fires with one ID, the server fires with the same ID, and the platform drops the duplicate. Without this, you report double the conversions.
• Hashed PII handling. User-matching data must be normalised before hashing. For email: lowercase, trim whitespace, then SHA-256. For phone: E.164 format (e.g., +14155552671), then SHA-256. Sending unhashed or incorrectly formatted data will result in poor match rates or API errors.
• Access tokens and permissions. Each platform requires an API access token tied to your ad account. Meta uses a system user token from your Business Manager. Google uses an OAuth credential tied to your Ads account. TikTok uses an access token from your Events API setup in TikTok Ads Manager.
• Testing and validation. Meta provides a Test Events tool in Events Manager. Google offers a diagnostics view in your conversion action settings. TikTok has an Event Tester in the Events API setup. Use these before going live to confirm events are arriving and being matched correctly.

Implementation complexity scales with how many platforms you run. Managing three separate CAPI integrations, each with their own token rotation, hashing requirements, and deduplication logic, adds meaningful engineering overhead to a media buying operation.

Conclusion

Conversion APIs are now a baseline requirement for any advertiser running meaningful budgets on Meta, Google, or TikTok. Browser pixels alone leave too much conversion signal on the floor, and ad platforms optimise worse when their data is incomplete.

Running S2S affiliate tracking and Conversion APIs together is not redundant. They serve different purposes: one tells your tracker what worked, the other tells the ad platform how to optimise. Both are needed for a complete measurement and optimisation setup.

If you want to see how ClickPattern handles server-side tracking and feeds conversion data accurately across your stack, book a demo and we'll walk through your specific setup.