Conversions API (CAPI)

The Conversions API is a server-side integration that sends conversion signals directly from a business’s web or app server to an advertising platform, without going through the user’s browser.

What the Conversions API Means in Marketing

For years, ad platforms measured conversions through browser-based pixels. A user completed a purchase, the pixel fired, and the platform knew the conversion happened. That worked well when browsers were relatively open. It stopped working well after Apple’s ITP changes limited cross-site cookie tracking, after iOS 14 required explicit opt-in for ad tracking, and after ad blockers became widespread.

The result was that platforms like Meta were losing visibility into a growing share of conversions. Advertisers saw their reported conversions drop while their actual sales stayed the same. Algorithms trained on incomplete data started making worse optimisation decisions.

The Conversions API solves this by moving the event tracking off the browser and onto the server. When a user buys something, your server sends the purchase event directly to the ad platform’s API. Ad blockers, browser settings and iOS privacy changes don’t touch server-to-server calls.

How the Conversions API Works

You configure your server to send event data: event type (purchase, lead, add to cart), a timestamp, order value, and hashed customer identifiers such as email address or phone number. The platform uses the hashed identifiers to match the event back to a user in its system.

Running the browser pixel alongside the CAPI is the recommended setup, called event deduplication. Both signals might fire for the same conversion. The platform deduplicates them using a shared event ID so the conversion is only counted once. This gives the algorithm the maximum number of matched signals without inflating conversion counts.

Conversions API Example

An e-commerce brand running Meta ads sees that about 30% of its conversions are going unattributed after iOS 14. After implementing CAPI alongside the pixel, it recovers a significant portion of those events. The campaign algorithm starts receiving better data, exits the learning phase faster, and the cost per purchase drops because the platform is now optimising against a more complete signal.

Why the Conversions API Matters for Marketers

Your ad platform’s algorithm is only as good as the data you feed it. A degraded signal means worse bidding decisions, longer learning phases and less accurate audience targeting. CAPI is the infrastructure fix that keeps your campaigns optimising against reality rather than an increasingly filtered version of it.