WooCommerce Revenue Does Not Match GA4

/**
 * One definition of order value, used by every destination.
 * Excludes tax and shipping. Change once here, not per integration.
 */
function propulse_ga4_order_value( WC_Order $order ) {
	$value = $order->get_total()
		- $order->get_total_tax()
		- $order->get_shipping_total();

	return round( max( 0, (float) $value ), 2 );
}

add_action( 'woocommerce_order_refunded', 'propulse_ga4_refund_event', 10, 2 );

function propulse_ga4_refund_event( $order_id, $refund_id ) {
	$order  = wc_get_order( $order_id );
	$refund = wc_get_order( $refund_id );

	if ( ! $order || ! $refund ) {
		return;
	}

	$payload = array(
		'event'     => 'refund',
		'ecommerce' => array(
			'transaction_id' => $order->get_order_number(),
			'value'          => round( abs( (float) $refund->get_amount() ), 2 ),
			'currency'       => $order->get_currency(),
		),
	);

	// Refunds happen in wp-admin, not in the customer's browser —
	// this must go to GA4 server-side via the Measurement Protocol.
	propulse_send_measurement_protocol( $payload );
}

/**
 * Send a server-side event to GA4 via the Measurement Protocol.
 * Requires the same client_id the browser session used.
 */
function propulse_send_measurement_protocol( array $payload ) {
	$measurement_id = 'G-XXXXXXXXXX'; // Your GA4 measurement ID.
	$api_secret     = 'YOUR_API_SECRET'; // GA4 Admin → Data Streams → Measurement Protocol.

	if ( ! $measurement_id || ! $api_secret ) {
		return false;
	}

	$client_id = $payload['client_id'] ?? propulse_ga4_client_id_from_order( $payload );
	if ( ! $client_id ) {
		return false;
	}

	$params = array( 'engagement_time_msec' => 100 );
	if ( ! empty( $payload['ecommerce'] ) ) {
		foreach ( $payload['ecommerce'] as $key => $val ) {
			$params[ $key ] = $val;
		}
	}

	$body = array(
		'client_id' => $client_id,
		'events'    => array(
			array(
				'name'   => $payload['event'],
				'params' => $params,
			),
		),
	);

	$url = sprintf(
		'https://www.google-analytics.com/mp/collect?measurement_id=%s&api_secret=%s',
		rawurlencode( $measurement_id ),
		rawurlencode( $api_secret )
	);

	$response = wp_remote_post(
		$url,
		array(
			'body'    => wp_json_encode( $body ),
			'headers' => array( 'Content-Type' => 'application/json' ),
			'timeout' => 5,
		)
	);

	return ! is_wp_error( $response ) && (int) wp_remote_retrieve_response_code( $response ) < 400;
}

function propulse_ga4_client_id_from_order( array $payload ) {
	// Store _ga cookie value on the order at purchase time for server-side sends.
	return $payload['client_id'] ?? '';
}