shopify checkout extensibility custom field broken

The actual problem

Checkout UI extensions fail silently after a theme or app update and kill conversion on paid traffic.

Do this

1. Reproduce checkout on mobile + desktop with a real payment method in test mode.
2. Checkout editor → disable custom extensions one by one until the error clears.
3. Check app changelogs for checkout extensibility breaking changes this week.
4. Re-enable only the extension that is load-bearing; leave experiments off paid campaigns.

Tools for this job

• Tillkiln

  Finds related checkout traps (guest, OOS, stacking) in the same pass

Related intents

• shopify abandoned checkout emails not sending
• shopify force account creation checkout dropoff