Conversions API (CAPI)
Conversions API, usually shortened to CAPI, is how Meta (Facebook and Instagram ads) learns that someone bought, from your own server instead of only from a pixel (a small snippet of code on your website that runs in the visitor's browser). Browsers can block that pixel, so the server message is a backup. CAPI recovers missed sale reports. It is not a fix for Apple's privacy limits on iPhones.
Theodor Lindfors, Founding Marketer ·
How Conversions API works
Let's take a drink brand as an example. They sell a low-sugar sports drink for active women over 50, mostly from their own website. The drink brand advertises on Meta, TikTok, and YouTube. A customer buys a $36 six-pack. The thank-you page tries to tell Meta about the order using the pixel (a small snippet of code in the visitor's browser). The customer's ad blocker stops the pixel. The drink brand's shop server still has the order. Conversions API (CAPI) is the backup: the server tells Meta directly, instead of relying on the customer's browser.
Let's take a drink brand as an example. They sell a low-sugar sports drink for active women over 50, mostly from their own website. A customer buys a $36 six-pack. The drink brand's server sends a Conversions API (CAPI) event: purchase, $36, plus a hashed email (a fingerprint of the customer's address, so Meta is not receiving the raw email), plus an event ID (a unique label for this order). Meta matches the customer to someone who saw a drink brand ad and credits the campaign. Most setups run Conversions API and the pixel together. If the pixel had also fired with the same event ID, Meta would keep one copy, not two.
Why CAPI matters
Browsers drop events. Ad blockers, short cookie lifetimes, and script failures all cost you conversions the platform never learns about. That hurts twice: a drink brand's reporting looks worse, and Meta's optimization has less to learn from.
The second part is the bigger deal. Conversion signal is what the algorithm optimizes against, so missing events make bidding worse, not just reports uglier. This is server-side tracking (sending events from your server instead of the visitor's browser) applied to one platform.
How to read a CAPI rollout
Reported conversions usually go up after Conversions API (CAPI) is switched on. That does not mean a drink brand sold more drinks. Mark the date, and compare platform-reported numbers against your own order data before you claim a win. If the shop processed 400 orders last week and Meta jumps from 280 reported purchases to 360 reported purchases, you recovered measurement. You did not invent 80 sales.
Watch deduplication carefully. Missing or mismatched event IDs will double-count purchases and hand you a ROAS (return on ad spend: credited sales divided by spend) that finance will not recognize.
Common CAPI mistakes
- Sending browser pixel events and Conversions API (CAPI) server events with no shared event ID, so a customer's $36 six-pack counts twice.
- Reading the reporting lift as real growth.
- Selling Conversions API (CAPI) internally as the answer to App Tracking Transparency (ATT, Apple's iOS permission prompt).
- Sending customer data you do not have consent to send.
Lemonado
How Lemonado helps around Conversions API
A Conversions API (CAPI) rollout changes what Meta sees, which changes what Meta reports. Lemonado keeps platform-reported conversions next to your own revenue data, so the jump in reported results does not quietly get read as growth.