window.dataLayer = window.dataLayer || [];
window.dataLayer.push({
  event: 'begin_checkout',              // name of the event. In this case, it always must be add_to_cart
  ecommerce: {                          
    currency: 'CZK',
    value: 29.98,                       // product price (with tax)
    items: [{                           // an array with a product (or multiple products) that was added to a cart
      item_name: 'VIP vstupenka',       // insert an actual product name
      price: '5500',                    // insert an actual product price. Number or a string. Don't include currency code                   
      quantity: '1'                     // product quantity of how many products were added to a cart
    }]
  }
});