client/lib/analytics/ad-tracking.js
function initFacebookAdvancedMatching() {
	const normalizedHashedEmail = getNormalizedHashedUserEmail( user );
	const advancedMatching = normalizedHashedEmail ? { em: normalizedHashedEmail } : {};

	debug( 'initFacebookAdvancedMatching:', advancedMatching );
	window.fbq( 'init', TRACKING_IDS.facebookInit, advancedMatching );

	/*
	 * Also initialize the FB pixel for Jetpack.
	 * However, disable auto-config for this secondary pixel ID.
	 * See: <https://developers.facebook.com/docs/facebook-pixel/api-reference#automatic-configuration>
	 */
	window.fbq( 'set', 'autoConfig', false, TRACKING_IDS.facebookJetpackInit );
	window.fbq( 'init', TRACKING_IDS.facebookJetpackInit, advancedMatching );
}
function initFacebookAdvancedMatching() {
	const normalizedHashedEmail = getNormalizedHashedUserEmail( user );
	const advancedMatching = normalizedHashedEmail ? { em: normalizedHashedEmail } : {};

	debug( 'initFacebookAdvancedMatching:', advancedMatching );
	window.fbq( 'init', TRACKING_IDS.facebookInit, advancedMatching );

	/*
	 * Also initialize the FB pixel for Jetpack.
	 * However, disable auto-config for this secondary pixel ID.
	 * See: <https://developers.facebook.com/docs/facebook-pixel/api-reference#automatic-configuration>
	 */
	window.fbq( 'set', 'autoConfig', false, TRACKING_IDS.facebookJetpackInit );
	window.fbq( 'init', TRACKING_IDS.facebookJetpackInit, advancedMatching );
}
See https://developers.facebook.com/docs/facebook-pixel/pixel-with-ads/conversion-tracking#advanced_match