What is Conversion API (CAPI)?

The Conversion API (CAPI) is a server-side interface provided by ad platforms to send conversion events directly from an advertiser’s or tracker’s backend, bypassing the user’s browser. The best-known implementation is Meta Conversions API; similar APIs exist for TikTok (Events API), Google (Enhanced Conversions), Pinterest, Snapchat, and others.

In arbitrage and performance marketing, CAPI complements or replaces pixel tracking when browser cookies are blocked, the user leaves before JavaScript fires, or the conversion happens offline (call, CRM, payment on the affiliate side). The server sends an HTTP request with event identifiers: event_id, fbp/fbc (Meta), hashed email/phone, IP, user agent, purchase value, and event type (Purchase, Lead, CompleteRegistration).

Why CAPI matters

Cookie resilience — iOS ATT, Safari ITP, and ad blockers reduce browser pixel coverage; server-side sending recovers part of the signal for optimization.
Deduplication — when pixel and CAPI run together, the platform matches events by event_id to avoid double counting.
Optimization quality — Meta and TikTok algorithms use richer data to train CPA/ROAS campaigns.

Integration with a tracker

Typical flow: click recorded by tracker → user converts → affiliate network sends a postback to the tracker → tracker or a side service fires the event to the ad platform. Source click IDs (fbclid, ttclid, gclid) and a consistent event_id must be passed. Without match keys, Meta’s Event Match Quality (EMQ) drops and optimization suffers.

Limitations

CAPI does not bypass privacy rules: EU traffic needs consent, PII is hashed (SHA-256). Server integration is harder than a pixel: access tokens, test events in Events Manager, and API error monitoring are required. In pure CPA arbitrage without CRM access, CAPI is often configured via the tracker or the network’s white-label integration.