WooCommerce Google Ads conversion tracking without duplicates

add_action( 'woocommerce_thankyou', function ( $order_id ) {
  $order = wc_get_order( $order_id );
  if ( ! $order || $order->get_meta( '_ag_dl_sent' ) ) {
    return; // already sent once for this order
  }
  $items = array();
  foreach ( $order->get_items() as $item ) {
    $product = $item->get_product();
    $items[] = array(
      'item_id'   => $product ? $product->get_sku() : $item->get_product_id(),
      'item_name' => $item->get_name(),
      'price'     => (float) $order->get_item_subtotal( $item, false ),
      'quantity'  => $item->get_quantity(),
    );
  }
  $data = array(
    'event'     => 'purchase',
    'ecommerce' => array(
      'transaction_id' => (string) $order->get_order_number(),
      'value'          => (float) $order->get_subtotal() - (float) $order->get_discount_total(),
      'tax'            => (float) $order->get_total_tax(),
      'shipping'       => (float) $order->get_shipping_total(),
      'currency'       => $order->get_currency(),
      'items'          => $items,
    ),
    'user_data' => array(
      'email'        => $order->get_billing_email(),
      'phone_number' => $order->get_billing_phone(),
    ),
  );
  $order->update_meta_data( '_ag_dl_sent', 1 );
  $order->save();
  echo '<script>window.dataLayer = window.dataLayer || [];'
    . 'dataLayer.push({ ecommerce: null });'
    . 'dataLayer.push(' . wp_json_encode( $data ) . ');</script>';
}, 20 );