Cart mutations reject unconfirmed writes in POS UI extensions 2026-10
Shopify developer change
MerchantDiff detected this entry in Shopify's official developer changelog on October 07, 2026.
This Shopify update is categorized as Action Required, API, Breaking API Change, POS Extensions, 2026-10.
What changed
POS reports the outcome of every cart write. Only a success result confirms that the cart changed. Earlier API versions resolve the mutation regardless of that result, so an app can't tell an applied write from a dropped one, and an app can show a fee or a discount as applied when the cart never changed. In 2026-10, these mutations reject unless POS confirms the write: bulkCartUpdate, removeLineItem, applyCartDiscount, addCartCodeDiscount, removeAllDiscounts, setCustomer, removeCustomer, addLineItemProperties, bulkAddLineItemProperties, removeLineItemProperties, setLineItemDiscount, bulkSetLineItemDiscounts, removeLineItemDiscount, addLineItemSellingPlan, and removeLineItemSellingPlan. updateLineItemQuantity is new in 2026-10 and rejects from its first release.
Who is affected
Apps that call any of the mutations above from a POS UI extension with api_version = "2026-10" or later. The change applies per extension, based on the API version the extension declares, not per store. Apps on 2026-07 and earlier keep the current behavior with no changes.
What action may be needed
Add rejection handling to every cart mutation your extension calls, then set api_version = "2026-10". Apps that bump without handling rejection will see handlers stop at the first unconfirmed write, which can leave a spinner on screen or skip a confirmation step. 2026-07 continues to work until it reaches the end of its support window under API versioning.
Use the official Shopify entry below as the source of truth for technical implementation details, affected APIs, migration instructions and deadlines.
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