Definition
A conversions API (CAPI) is the server-to-server interface an advertising platform provides so advertisers can send conversion and event data directly from their servers instead of, or alongside, the platform's browser pixel. Meta, TikTok, Google, Snapchat and others offer one.
The advertiser sends events — registration, deposit, purchase — with parameters and hashed identifiers (email, phone, IP, user agent, click ID) that the platform uses to match the event to a user and to attribute it to an ad.
CAPI exists because browser-side pixels miss a growing share of events due to tracking prevention, ad blockers and cookie restrictions. Sending the same events server-side recovers much of that signal, which improves attribution accuracy and, importantly, the quality of the conversion data the platform's optimisation algorithms learn from.
Most setups run pixel and CAPI together with event de-duplication so each conversion is counted once.
In context
For iGaming advertisers operating where paid social and search allow the vertical, CAPI is close to essential because the value events that matter — first deposit, qualifying deposit, deposit value — are exactly the ones most degraded by client-side loss, and feeding them reliably to the platform is what lets value-based bidding and optimisation work. An operator sending clean, well-matched FTD events with value through CAPI will generally see better campaign efficiency than one relying on a decaying pixel.
The compliance requirements are strict and specific. CAPI sends personal data (even hashed) to a third-party platform, so it needs a lawful basis and, for most parameters, the user's consent — a CAPI integration that fires regardless of the cookie banner choice is a data-protection breach.
Advertising rules still apply to what is optimised toward and to audience construction, and responsible-gambling suppression must exclude self-excluded and opted-out users before events are sent. Sending events for players who should not be marketed to, or building lookalikes from them, is a serious failure.
Used within consent and gambling-advertising rules, CAPI is a legitimate accuracy improvement; used to bypass tracking prevention or consent, it is the same violation as any covert tracking, just server-side.
Worked example
An operator adds Meta CAPI alongside its pixel, sending de-duplicated FTD events with deposit value and hashed identifiers, but only for users who consented to advertising cookies; others are excluded server-side. Match quality rises, value-based campaigns optimise better, and self-excluded users never enter the event stream or any lookalike seed.
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