A Conversions API (CAPI) is a server-to-server route an advertising platform exposes so conversion events can be sent to it directly from the advertiser's own systems, instead of from a script in the visitor's browser. Meta's is the one usually meant by CAPI, and other platforms run their own under their own names and rules. Because the request does not depend on the platform's script loading in the browser, the event survives a blocked or failed page, though it is only credited to a campaign when the identifying data sent with it is enough to match a person.
Why it matters for agencies
For the client this lands in the platform's conversion count and in how well campaigns bid: an event that never reaches Meta or LinkedIn is missing from the examples the bidding learns from, not just from a report. Ad blockers alone strip 30-40% of browser events, which is why the server route exists. Arriving is not the same as being credited, though. Meta accepts a server event carrying one customer information parameter and then scores how well it can be matched, out of 10, so an event with little more than an IP address is accepted and barely matched.
What teams get wrong
The expensive mistake is adding the server route while the browser tag keeps firing. Meta deduplicates only when the event name and the event ID match, and only within 48 hours of the first copy arriving. LinkedIn needs a separate conversion rule per data source and keeps the browser copy. Miss it and reported conversions rise while the business stands still, so cost per acquisition improves on paper and nobody escalates a number that looks like a win. Meta's own guidance is to send the same events through both the pixel and the API, so the duplication is intended and the shared ID is what keeps the count honest.
The second is calling it done at one platform. LinkedIn's Conversions API attaches events to a conversion rule, and only campaigns tied to that rule are attributed. Google Ads does not use the term at all, its server path is a conversion upload through the Google Ads API. The third is treating the server as a way around the banner. Meta's Business Tools Terms require verifiable consent where the law asks for it, and Archon Labs treats a Conversions API as a change of delivery, never a change of permission.
