Shopify POS changes discount values and cart updates

Shopify has announced two POS extension changes that app teams should test separately: how percentage discounts are represented, and how failed or uncertain cart updates are reported. The first depends on the POS app version; the second depends on the extension’s API version.

A percentage is no longer returned as money

The 7 October discount announcement says POS 11.15 corrects Discount.amount for discounts whose type is Percentage. A 25% reduction on a $200 line now returns 25; earlier POS versions returned 50, the amount of money deducted.

This affects every POS UI extension API version. Keeping an older API version will not retain the previous behaviour. Fixed-amount and code discounts are unchanged, including percentage-based discounts represented as Code.

App teams should review savings displays, loyalty calculations and any integration treating a percentage amount as currency. Test both cart and line discounts, automatic discounts and workflows that send the cart back through bulkCartUpdate. Stores still running POS 11.14 or earlier need compatibility handling until those devices are upgraded.

Unconfirmed cart updates can reject

A separate 7 October release note changes cart mutations in POS UI extensions using API version 2026-10. A call now rejects if POS does not confirm the write. Previously, an app could continue as though its change had succeeded.

There are two distinct cases: POS can refuse the update, leaving the cart unchanged, or fail to confirm the outcome, when a partial change remains possible. In the second case, read the cart before retrying. Other validation errors can also reject a mutation.

Developers should handle rejected promises at each cart-write call before adopting 2026-10, including cleanup of loading indicators and clear staff feedback. Extensions on 2026-07 or earlier retain their previous behaviour within their support window.

What merchants should ask their app vendor

Ask whether loyalty and custom-discount apps have been tested on the POS version used across your locations, and whether their cart-update handling is ready for the extension API version they declare. Those are two separate compatibility questions.

Our recommendation is to rehearse a percentage discount and an interrupted cart update in a controlled test. Check the receipt, displayed savings and points calculation against the intended offer. The release notes identify risks in app logic; they do not prove that your store has charged customers incorrectly.