Tracking

Conversion API

CAPI

In short

A Conversion API (CAPI) is an interface that sends conversions directly from server to server to ad platforms like Meta or Google, without the browser.

Also known as: Conversions API, Meta Conversions API

A Conversion API (CAPI for short) is an ad platform interface that lets you send conversions directly from your server to the platform – without going through the user's browser. The best known is the Meta Conversions API; Google Ads, TikTok and LinkedIn offer comparable interfaces.

How the Conversion API works

Instead of a tracking pixel firing in the browser, your server (or a tool) sends an API request to the platform. It contains:

  • Event: e.g. lead, purchase or closed deal
  • Timestamp and optionally value and currency
  • Matching data: click IDs like fbclid (or the fbc value derived from it) or gclid, plus email address, phone number and name pseudonymized with hashing (SHA-256)
  • Event ID: for event deduplication with the pixel

The more matching data you send, the better the platform can match the event to a user and thus to an ad click. Meta rates this with its Event Match Quality score.

Example

An insurance broker generates 300 leads a month from Meta, 24 of which become customers. The pixel only reports the leads it sees in the browser. Through the Conversion API, the 24 closed deals are also sent – with the commission as value, weeks after the click. Meta learns which audiences actually bring in customers instead of just optimizing for cheap leads.

Conversion API for lead generation

The biggest lever is offline conversions: deals closed in the CRM and payments never happen in the browser and can only be reported through a Conversion API. Value-based bidding needs exactly these values.

With the LeadMetrics Conversion API you send leads, purchases, trials, subscription events, won or lost deals and custom metrics to Meta, Google Ads, TikTok and LinkedIn. Per project you decide which LeadMetrics event maps to which platform event, and whether only attributed data or (for Meta and TikTok) all data is sent. Data comes from sources like HubSpot or Stripe, and every lead has a log of the events sent.

Common mistakes

  • No event ID: Pixel and CAPI send the same event and the platform counts it twice.
  • Unhashed data: Contact data must be normalized and hashed before sending.
  • Only sending leads: If you don't report the closed deal, you're giving away your most valuable signal.

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Frequently asked questions

For reliable data: yes. The pixel loses conversions to ad blockers and cookie restrictions. The Conversion API delivers those events server side. When both run in parallel, a shared event ID makes sure nothing is counted twice.

Guides on this topic

Metrics8 min read

Measure Real ROAS in Lead Generation: From Click to Closed Deal

How to measure real ROAS in lead generation: attribute CRM revenue to campaigns, read CPL, CPA and ROAS correctly and send deal values back to Meta and others.

Read guide
Tracking7 min read

Campaign Tracking with UTMs and Click IDs: Setup Guide

Set up clean campaign tracking: a UTM naming convention, dynamic parameters in Meta and Google Ads, click IDs, common mistakes and how to test it all.

Read guide
Metrics7 min read

Social Media KPIs for Lead Generation: Which Metrics Matter

The key social media metrics for lead campaigns on Meta, Instagram, TikTok and LinkedIn: from reach and CTR to cost per lead, cost per acquisition and ROAS.

Read guide

Articles on this topic

Related terms

All terms

Server-Side Tracking

Server-side tracking sends tracking data to ad and analytics platforms from a server instead of the browser – more robust and under your control.

Tracking Pixel

A tracking pixel is a snippet of code from an ad platform that captures page views and conversions in the browser and reports them to Meta, Google and others.

Event Deduplication

Event deduplication makes sure a conversion sent through both the pixel and the Conversion API is only counted once by the ad platform.

Event Match Quality

Event Match Quality (EMQ) is a Meta score from 0 to 10 that rates how well your server events can be matched to a Meta account using customer data.

Offline Conversions · Reporting deals that happen off your website back to ad platforms

Offline conversions are conversions that don’t happen on your website – like a closed deal in your CRM – and are sent back to ad platforms like Meta.

Client-Side Tracking

Client-side tracking captures user actions with JavaScript directly in the browser and sends them from there to analytics and ad platforms.