Quick answer
Checkout Extensibility does not just change how checkout is customized. It changes where tracking, Thank You page customizations, Order Status page customizations, checkout.liquid work, and Additional Scripts work. Anything living in old checkout surfaces needs to be reviewed and replaced.
Symptom
A store upgrades or is preparing to upgrade and then discovers tracking, custom Thank You page content, checkout.liquid code, post-purchase scripts, or Order Status page behavior no longer works the same way.
Most likely causes
- Additional Scripts are deprecated/replaced. Shopify directs tracking and analytics customizations toward pixels.
- checkout.liquid customizations need replacement. Old Liquid customizations do not map one-to-one to the new editor.
- Thank You and Order Status pages are upgraded separately. Existing customizations must be reviewed in the upgrade guide.
- Apps may be incompatible. Apps need compatible blocks or pixels for the new pages.
- PII access and pixel behavior changed. Shopify’s docs call out impacts on scripts and customer data.
Quick checks
- Go to Settings → Checkout and open the upgrade notice/report.
- Review the personalized upgrade guide.
- List every existing Additional Script, checkout.liquid customization, tracking script, and app customization.
- Mark each item as app block, web pixel, app pixel, UI extension, Shopify Function, or remove.
- Test purchase tracking before and after upgrading.
Theme, app, or code checks
- Look specifically for Google Ads, Meta, GTM, affiliate, review, post-purchase, survey, warranty, and ERP scripts.
- Review incompatible apps in the upgrade guide.
- Do not assume a theme.liquid script will cover checkout/thank you behavior.
- For Plus stores, review checkout customizations separately from Thank You/Order Status customizations.
When to stop guessing
Stop treating this like a theme update. If revenue tracking or checkout logic is involved, make a migration checklist and test with real orders or test transactions before publishing the upgraded pages.
Prevention checklist
- Keep a pre-upgrade inventory of scripts and customizations.
- Move tracking to app pixels or custom pixels where appropriate.
- Use Shopify’s upgrade guide instead of guessing from old theme files.
- Run test orders and compare Google/Meta/analytics events before and after.