Meta’s Conversions API match rate directly determines how many conversions get attributed to your campaigns. A match rate below 40% means more than half of your conversions are invisible to Meta’s attribution, making ROAS calculations unreliable. This guide identifies the seven customer information parameters that have the highest impact on match rates and explains exactly how to implement each one.

How Meta Matching Works

When a server event arrives at Meta’s CAPI endpoint, Meta attempts to match it to a user in its database using a combination of identity signals. The Event Match Quality (EMQ) score in Meta’s Events Manager shows a number from 0 to 10 — 7+ is good, 5-6 is moderate, below 5 means significant events are unmatched. Meta hashes all personally identifiable parameters before matching using SHA-256.

Parameter 1: Email Address (em)

Email is the single highest-impact matching parameter. A single well-formatted, SHA-256 hashed email address can bring an EMQ score from 3 to 7 by itself. Normalise before hashing: trim whitespace, convert to lowercase.

const crypto = require('crypto');
function hashEmail(email) {
  return crypto.createHash('sha256').update(email.trim().toLowerCase()).digest('hex');
}
user_data: { em: hashEmail(customerEmail) }

Parameter 2: Phone Number (ph)

Phone numbers are the second highest-impact parameter. Normalise to E.164 format before hashing: remove all non-numeric characters except the leading plus sign, and ensure the country code is included. A UK number should be +441234567890. Many implementations fail because they hash the phone number as collected from a form field which may include spaces, dashes, or parentheses in inconsistent formats.

Parameter 3: Facebook Browser ID (fbp)

The fbp cookie is set by Meta’s pixel and contains a unique browser identifier. When a CAPI event includes the fbp value, Meta can match the server event to the same browser session that saw an ad. This parameter does not require hashing. Read the fbp value from the _fbp cookie in your server code and pass it through to your CAPI event. If the fbp cookie is missing, simply omit the parameter.

Parameter 4: Facebook Click ID (fbc)

The fbc value is derived from the fbclid URL parameter that Meta appends to all ad click URLs. Capture it when users land from a Facebook ad and store it in a first-party cookie before it disappears from the URL. The fbc format is fb.{version}.{creation_time}.{fbclid_value}. Send the _fbc cookie value in your CAPI events without hashing.

Parameters 5-7: Name, External ID, Client IP and User Agent

First and last names as separate SHA-256 hashed parameters improve match rates when combined with other parameters. The external_id is your own user identifier — typically a customer ID from your CRM — hashed with SHA-256. The client_ip_address and client_user_agent parameters are extracted from the original user’s HTTP request headers and passed through to CAPI without hashing. Implementing all seven parameters ensures you are sending everything Meta can use. Check your EMQ scores in Events Manager after implementation to verify improvement.