transaction_products.push({
  item_name: product_name,
  item_id: product_sku,
  price: product_price,
  quantity: product_quantity
});

dataLayer.push({
  event: 'purchase',
  ecommerce: {
    transaction_id: transaction_id,
    affiliation: transaction_affiliation,
    value: transaction_total,
    shipping: transaction_shipping,
    tax: transaction_tax,
    currency: transaction_currency,
    items: transaction_products
  }
});