GA4 purchase event not firing after Shopify checkout extensibility

GA4 recorded purchases for years, then one day the purchase line drops close to zero and stays there. Orders keep coming in. Shopify looks normal. Nothing in GA4 warns you. For most stores in 2025 and 2026, the cause is the same: Shopify's move to checkout extensibility removed the place where the GA4 purchase code used to live.

This guide explains what changed, why it broke GA4, the three ways to rebuild the purchase event, a working custom pixel you can adapt, and how to test it. For the full diagnosis of missing purchases beyond this one cause, see GA4 missing Shopify purchases.

What changed in Shopify checkout

Checkout extensibility is Shopify's locked-down checkout. Instead of editing checkout templates and pasting scripts, merchants extend checkout with apps, UI extensions and pixels that run in a sandbox. It rolled out in stages:

The last change happened automatically. Stores were upgraded whether or not they had moved their tracking, which is why so many GA4 properties lost purchases at the end of August 2026.

Why the GA4 purchase stopped

On older setups, the purchase usually came from one of these, and all of them are now gone:

• A gtag snippet in Additional Scripts that sent the purchase when the Thank you page loaded.
• A GTM data layer push on the Thank you page that a GA4 purchase tag listened for.
• The theme GTM container. Checkout pages never ran theme code, and with the old scripts gone there is nothing left to load it.

Everything before checkout, like product views and add to cart, often still works because it runs in the theme. That is why the drop shows up in purchases first.

Three ways to rebuild it

Whichever you choose, use only one. A common mistake after the upgrade is adding the Google and YouTube app while a custom pixel also sends purchases, which swaps missing purchases for duplicated ones.

A GA4 purchase custom pixel

Custom pixels listen for Shopify's standard events. The one that matters here is checkout_completed, which fires once per order. This example sends a GA4 purchase with items, reuses the storefront's client ID so the order keeps its traffic source, and sets the real page URL instead of the sandbox address:

// Shopify admin: Settings > Customer events > Add custom pixel
// Replace G-XXXXXXXXXX with your GA4 measurement ID.
const GA4_ID = 'G-XXXXXXXXXX';

const s = document.createElement('script');
s.src = 'https://www.googletagmanager.com/gtag/js?id=' + GA4_ID;
s.async = true;
document.head.appendChild(s);

window.dataLayer = window.dataLayer || [];
function gtag() { dataLayer.push(arguments); }
gtag('js', new Date());

analytics.subscribe('checkout_completed', async (event) => {
  const c = event.data.checkout;

  // Reuse the storefront's GA4 client ID so the purchase keeps its source.
  const ga = await browser.cookie.get('_ga'); // GA1.1.1234567890.1700000000
  const clientId = ga ? ga.split('.').slice(-2).join('.') : undefined;

  gtag('config', GA4_ID, {
    send_page_view: false,
    client_id: clientId,
    page_location: event.context.document.location.href,
  });

  gtag('event', 'purchase', {
    transaction_id: c.order?.id,
    value: Number(c.totalPrice?.amount),
    tax: Number(c.totalTax?.amount || 0),
    shipping: Number(c.shippingLine?.price?.amount || 0),
    currency: c.currencyCode,
    items: c.lineItems.map((li) => ({
      item_id: li.variant?.sku || li.variant?.id,
      item_name: li.title,
      item_variant: li.variant?.title,
      price: Number(li.variant?.price?.amount),
      quantity: li.quantity,
    })),
  });
});

A few things to adjust before you rely on it:

• Revenue definition. totalPrice includes tax and shipping. If your reports use subtotal, send subtotalPrice instead, and use the same definition everywhere.
• Transaction ID. Use the same order identifier your other tools use, so you can match GA4 to Shopify later.
• Customer privacy. In the pixel's settings, set the permission to require analytics consent if your store shows a cookie banner. Our Consent Mode v2 guide covers the Google side.
• Upsell apps. With a post-purchase upsell, checkout_completed fires on the first upsell page instead of the Thank you page. Listening for the event rather than a page view keeps it working.
• Multi-currency stores. With Shopify Markets, checkout amounts are in the currency the customer paid in. Send that currency code with those amounts and GA4 converts them to your reporting currency. Mixing the store currency code with customer currency amounts is a common source of wrong revenue.
• Connect the pixel. A saved custom pixel does nothing until you click Connect. Customer events shows each pixel's status, so check it says Connected after every edit.

Rebuild the rest of the checkout funnel

The purchase is the event everyone notices, but the checkout steps before it broke at the same time. Without them, GA4's checkout funnel report goes blank and you can't see where buyers drop off. Shopify's standard events map to GA4's recommended ecommerce events like this:

Each one is another analytics.subscribe call in the same pixel, sending the same items array. Keep product views and add to cart wherever they run today, usually the theme or the Google and YouTube app, so nothing fires twice. Once all four checkout events arrive, GA4's funnel exploration shows exactly which step loses the most buyers, which is often more useful than the purchase count itself.

Test it end to end

1. Turn on DebugView. In GA4, open Admin, DebugView. Add debug_mode: true to the purchase event while testing, then remove it.
2. Place a real order with a 100% discount code and free shipping.
3. Watch the network. In your browser's developer tools, filter the Network tab for collect and find the request with en=purchase. Check the value, currency and transaction ID.
4. Check the source. Arrive on the store through a URL with UTM parameters before ordering. The purchase in GA4 should keep that source instead of showing as direct.
5. Watch for a week. Compare GA4 purchases with Shopify online orders each day. A healthy setup captures 90% or more. The GA4 vs Shopify revenue guide explains how to read the gap that remains.

Common questions

Owais Alam

Freelance data and analytics engineer and founder of Good Numbers. Top Rated on Upwork. Specializes in GA4, Google Tag Manager, BigQuery, server-side tracking and Shopify attribution.

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