Checkout Extensibility and What Broke Your Old Tracking Scripts
Why Shopify's move to checkout extensibility disabled checkout.liquid scripts and how to replace them properly.
Written by Mantas Jurgutis — Founder, Adsify — builds the Google & Meta automation merchants use daily
Editorially reviewed by Adsify Editorial on April 12, 2026 — Reviewed against Shopify, Google Ads and Meta official documentation.
What changed
Shopify moved all Shopify Plus merchants, and eventually all merchants, off checkout.liquid customization and 'additional scripts' in checkout settings, replacing them with checkout extensibility: a system of UI extensions and Web Pixels built on Shopify's newer APIs. Shopify's own migration documentation set deadlines after which checkout.liquid-based customizations stopped rendering, which is why scripts that worked for years suddenly disappeared from checkout with no warning to the storefront visitor, but a very noticeable drop in tracked conversions to the merchant.
Why Shopify made this change
checkout.liquid allowed arbitrary script injection directly into the page handling payment information, which was a growing PCI-DSS and security surface area, and it also meant every checkout customization had to be manually rebuilt whenever Shopify updated checkout's underlying markup. Checkout extensibility decouples customizations into sandboxed extension points and a separate Web Pixel API for tracking, so Shopify can update checkout's core code without breaking every merchant's custom scripts.
What specifically stopped working
Any tracking pixel that was pasted into Settings > Checkout > Additional scripts, including manually added Google Ads remarketing tags, Meta pixel base code, TikTok pixel snippets, or custom GA4 event pushes, stopped executing on the checkout and thank-you pages once checkout.liquid support ended for the store. If those scripts were the only source of purchase-event tracking, the store's reported conversions for Google Ads and Meta effectively dropped to near zero, even though sales continued normally in Shopify.
The replacement: Web Pixel API
The direct replacement is the Web Pixel API, accessed either through an app that registers a first-party pixel or through Settings > Customer events > Add custom pixel for a hand-written pixel. Unlike additional scripts, a Web Pixel runs in a sandbox without DOM access, subscribing to standardized events like checkout_completed instead of reading page elements directly, which is a fundamentally different programming model, not a drop-in replacement of the old script.
The replacement for UI changes
If the old checkout.liquid script wasn't tracking anything but instead changing checkout's appearance or behavior, like adding a custom field, a trust badge, or reordering elements, that logic needs to move to checkout UI extensions (for Shopify Plus and eligible plans) or Shopify Functions for business logic like custom discounts and shipping rules. These are separate APIs from Web Pixels and typically require more development effort than tracking migration alone.
Why some merchants didn't notice immediately
Stores that already had Google's or Meta's official Shopify sales channel apps installed were largely insulated, because those apps migrated to Web Pixel-based tracking on Shopify's behalf ahead of the checkout.liquid cutoff. The merchants who got surprised were typically ones running a marketing agency's custom-pasted script, an older Google Tag Manager container injected manually, or a legacy pixel from an app that had since been abandoned by its developer.
Diagnosing a post-migration drop
If reported ad conversions dropped sharply on a specific date with no change in actual sales, check that date against Shopify's checkout extensibility migration deadlines for your plan and store creation date, and check Settings > Customer events for whether the expected pixel is even present in that list; if it's not listed there, it isn't running at all on the current checkout.
Migrating a custom GTM setup
Google Tag Manager containers that were injected via checkout.liquid need to be replaced with a GTM setup that runs through a custom Web Pixel, subscribing to Shopify's standard events and pushing them into GTM's dataLayer equivalent inside the sandbox, or more commonly, replaced entirely by the official Google & YouTube Shopify app's native Enhanced Conversions and conversion tracking, which doesn't require GTM at all for basic Shopify conversion tracking.
Order status page differences
checkout.liquid-era scripts often specifically targeted the order status (thank-you) page to fire a purchase event once, after payment. The Web Pixel API's checkout_completed event serves the equivalent purpose but fires from the sandbox rather than from a script embedded in the thank-you page's HTML, and it fires once per completed checkout with structured order data rather than requiring the developer to scrape values out of the page DOM.
Testing after migration
After migrating, place a real test order and verify in Settings > Customer events that the new pixel logged checkout_completed with correct values, then confirm the event arrived in Google Ads diagnostics or Meta Events Manager's Test Events tool. Because the failure mode here is silent (no error shown to the merchant, no error shown to the customer), testing is the only reliable way to confirm the migration actually preserved tracking rather than merely removing the old broken script.
Where third-party apps help
Apps like Adsify that maintain their own Web Pixel and server-side event delivery are built against the current checkout extensibility model rather than checkout.liquid, so merchants adopting or re-platforming their tracking through an actively maintained app avoid repeating this migration pain the next time Shopify changes checkout's underlying implementation.
What to check right now
Even if your store migrated years ago, check Settings > Checkout to confirm 'Additional scripts' no longer exists as an active field with content in it (Shopify may show it as read-only or removed depending on plan), and cross-reference every pixel you believe is tracking your store against the live list in Settings > Customer events. Any tracking vendor not appearing there is not currently instrumented on checkout.