GA4 E-commerce Tracking with dataLayer: Full Setup Guide

How it works

GA4 builds e-commerce reports only from recommended events with fixed names and parameters. The flow:

1. On a user action, the site code calls dataLayer.push with an event and an ecommerce object.
2. A Google Tag Manager trigger catches the event.
3. A GA4 event tag sends it along with the e-commerce data.

Developers own the dataLayer, marketers own GTM and reports. Agree on the structure up front and write it down in a spec.

Which events you need

There are also view_promotion and select_promotion for banners, and add_to_wishlist. The minimum for a working funnel: view_item, add_to_cart, begin_checkout, purchase.

Item and event parameters

Every event carries an items array. Each item requires item_id or item_name; the rest is optional but recommended:

• item_id, item_name: SKU and name, identical across all events;
• price: unit price as a number, not a string;
• quantity;
• item_brand, item_category … item_category5, item_variant;
• item_list_id, item_list_name, index: which list the item appeared in and at what position;
• discount, coupon.

At the event level: currency in ISO 4217 format (for example UZS or USD) and value. Without currency, revenue is not recorded. purchase requires a transaction_id; tax, shipping and coupon are optional.

dataLayer example

Clear the ecommerce object before every e-commerce event; otherwise data from the previous event can carry over to the next one.

window.dataLayer = window.dataLayer || [];
dataLayer.push({ ecommerce: null });
dataLayer.push({
  event: 'purchase',
  ecommerce: {
    transaction_id: 'ORD-10452',
    currency: 'UZS',
    value: 450000,
    shipping: 30000,
    items: [{
      item_id: 'SKU-201',
      item_name: 'Travel mug',
      item_category: 'Kitchen',
      price: 150000,
      quantity: 3
    }]
  }
});

Decide in advance whether value includes shipping and tax, and apply the rule the same way everywhere.

GTM setup

1. Create a Custom Event trigger with a regex such as view_item|add_to_cart|begin_checkout|purchase|refund.
2. Create a Google Analytics: GA4 Event tag with the event name {{Event}}.
3. In the tag's advanced settings, enable Send Ecommerce data with Data Layer as the source.
4. Attach the trigger and publish the container after testing.

One tag covers all events as long as the dataLayer follows Google's recommended structure.

Refunds

• Full refund: a refund event with the original order's transaction_id, currency and value.
• Partial refund: the same plus an items array with the refunded items and quantities.

Refunds usually happen in an admin panel or CRM, not in the buyer's browser. So they are easier to send server-side via the Measurement Protocol or upload through data import rather than through the dataLayer.

How to validate the data

• GTM Preview: the event fired and the Data Layer tab shows the correct structure.
• GA4 DebugView: the event arrived with its parameters and items.
• Backend reconciliation: weekly, compare order count and revenue in GA4 with your database. Small gaps are normal (blockers, declined cookies); large gaps point to a bug.

Common mistakes:

• Duplicate purchase events when the thank-you page reloads. Send the event once, for example using a server-side flag.
• Price as a string, or with spaces and a currency symbol.
• Different item_id on the product page and in the purchase, which splits product reports.
• Missing currency, so revenue shows as zero.
• An external payment gateway breaks the session: add its domain to the unwanted referrals list.