Meta Conversions API: How to Set It Up and Deduplicate Events

The short answer: how it works

Meta Conversions API (CAPI) sends events (lead, purchase, sign-up) to Meta from a server instead of the browser. CAPI usually runs alongside the pixel:

• the pixel captures browser events and on-site behaviour;
• CAPI sends the same events from the server and delivers them even when the browser request is blocked or lost;
• Meta deduplicates the pairs and counts each event once — provided you send matching identifiers.

The server can also send events that never happen in the browser, such as a payment confirmed in the CRM.

Integration options

Deduplication with event_id

Meta treats two events as duplicates when their event_name and event_id match and they belong to the same pixel. So the ID must be generated once and sent through both channels.

In the browser:

const eventId = crypto.randomUUID();
fbq('track', 'Lead', { value: 0, currency: 'USD' }, { eventID: eventId });
// send the same eventId to your server together with the form data

On the server, the same value goes into event_id:

{
  "data": [{
    "event_name": "Lead",
    "event_time": 1760000000,
    "event_id": "same-uuid",
    "action_source": "website",
    "event_source_url": "https://example.com/contacts",
    "user_data": {
      "em": ["<sha256 email>"],
      "ph": ["<sha256 phone>"],
      "client_ip_address": "203.0.113.10",
      "client_user_agent": "Mozilla/5.0 ...",
      "fbp": "fb.1.1700000000000.123456789",
      "fbc": "fb.1.1700000000000.AbCdEf"
    }
  }]
}

Common causes of duplicates: different event name spelling (Lead vs lead), event_id generated separately in the browser and on the server, or the server event sent with too long a delay.

Event Match Quality

Event Match Quality (EMQ) is a score in Events Manager that shows how well Meta can match your server events to user accounts. The higher it is, the more accurate attribution and optimisation become.

How to improve it:

• send email and phone when the user has provided them;
• send fbp (the _fbp cookie) and fbc (the _fbc cookie or the fbclid URL parameter);
• include the client's IP address and user agent, not your server's;
• use external_id — your internal user ID, identical in the pixel and CAPI.

Hashing customer data

Personal data (email, phone, name, city and so on) must be normalised and hashed with SHA-256 before sending. Do not hash IP, user agent, fbp or fbc.

import { createHash } from 'node:crypto';

const sha256 = (v) => createHash('sha256').update(v).digest('hex');

const em = sha256(' User@Example.com '.trim().toLowerCase());
const ph = sha256('+998 90 123-45-67'.replace(/\D/g, '')); // digits only, with country code

A normalisation mistake (a space, a capital letter, a plus sign in the number) produces a different hash and no match.

Verifying in Events Manager

1. Open Test Events, copy the test_event_code and add it to server requests while debugging.
2. Perform an action on the site and confirm the event arrives from both the browser and the server.
3. In the event details, check the deduplication status: the pair should be shown as handled.
4. After a while, review EMQ and the Diagnostics tab for errors and recommendations.
5. Remove test_event_code before going to production.

Request format details are in the Meta documentation.