The Conversions API is a way for a server to tell an ad platform directly that a conversion happened, instead of relying only on a pixel in the visitor’s browser. If the browser blocks the pixel, the server message still arrives, so the platform keeps learning which ads bring buyers.
A conversions API is a server-to-server endpoint an advertising platform offers for receiving conversion events. Meta’s Conversions API, usually called CAPI, is the best-known one; TikTok’s Events API, Snap’s Conversions API and Google’s enhanced conversions and offline conversion imports work on the same principle. Each event carries a name, a time, the source URL and customer information parameters such as a hashed email or phone, Meta’s click identifier fbc and browser identifier fbp, the IP address and the user agent, which the platform uses to match the event to someone who saw or clicked an ad.
Pixels run in the browser and lose events to ad blockers, browser restrictions, refused consent and pages closed before the script loads. The server path avoids most of that. Platforms therefore recommend a redundant setup in which the pixel and the API send the same events and the platform removes duplicates. Meta merges a browser event and a server event that share the same event_name and event_id when they arrive within 48 hours of the first; mismatched IDs mean every conversion is counted twice.
For affiliates the conversion usually happens on the advertiser’s site, where they cannot place a purchase pixel. The standard workaround is the tracker: the network’s postback reaches the affiliate’s tracker, which forwards the conversion to Meta or TikTok through their server API together with the click identifiers it stored at the moment of the click. Keitaro, Voluum, RedTrack and similar trackers support these integrations, and they are how media buyers feed real sales, not just clicks, back into platform optimisation.
Match quality decides how useful the data is: the more reliable identifiers an event carries, the more conversions the platform can attribute and learn from. Personal data has to be hashed the way the platform specifies, collected with consent where the law requires it and limited to what the platform’s business terms allow, which exclude sensitive categories of information. Sending only approved conversions, rather than every pending one, keeps the algorithm aimed at customers the advertiser will actually pay for.
A media buyer sends Meta traffic to a prelander for a CPA offer: 3,600 USD spent in a week and 120 approved conversions in the network report.
| Setup | What Meta optimises for | Sales Meta can see |
|---|---|---|
| No conversion signal | landing page views | 0 |
| Pixel on the prelander button | clicks towards the offer | 0 |
| Tracker forwards approved postbacks via CAPI with stored fbc and fbp | purchases | 104 of 120 matched |
Only the third setup tells Meta who actually bought, so delivery shifts toward people who resemble buyers rather than clickers, and the platform’s reported cost per purchase (about 34.60 USD) becomes comparable with the real one (30 USD). The 16 unmatched sales came from clicks where no Meta click identifier was stored, for example after in-app browser redirects. Numbers are illustrative.
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A server-side interface that lets advertisers send conversion events from their server straight to an ad platform such as Meta, instead of only through a browser pixel.
Meta recommends running both with deduplication: the pixel captures browser signals and the API recovers events the browser loses.
It keeps one copy when a browser event and a server event with the same event name and event ID arrive within 48 hours of the first one.
Yes, through their tracker. The network postback reaches the tracker, which forwards the conversion to the platform with the click identifiers stored at the click.
References are listed as plain text on purpose; look them up by title and publisher. Updated: 2026-10-09.
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