---
title: "Shopify POS UI extensions 2026-10 cart mutations reject unconfirmed writes: 2026-10-07 | Harbyn"
description: "Shopify POS UI extensions 2026-10 cart mutations reject unconfirmed writes, announced Oct 7, 2026."
canonical: "https://harbyn.com/changes/shopify/2026-10-07-cart-mutations-reject-unconfirmed-writes-in-pos-ui-extensions-2026-10"
last-updated: 2026-10-07
---

# Shopify POS UI extensions 2026-10 cart mutations reject unconfirmed writes

Markdown version of <https://harbyn.com/changes/shopify/2026-10-07-cart-mutations-reject-unconfirmed-writes-in-pos-ui-extensions-2026-10>.

Breaking change - Shopify. medium severity. In effect.

In POS UI extensions using API version 2026-10 or later, cart mutations reject when POS does not confirm the write; previously, mutations resolved regardless. Apps must handle rejected promises. Extensions on 2026-07 and earlier are unaffected. updateLineItemQuantity rejects from its first release in 2026-10.

## Facts

| Fact | Value |
| --- | --- |
| Vendor | [Shopify](https://harbyn.com/vendors/shopify.md) |
| Kind | Breaking change |
| Severity | medium |
| Status | In effect |
| Announced | Oct 7, 2026 |
| Added to Harbyn | Oct 7, 2026 |
| Lead time | No dated deadline |
| Symbols | `bulkCartUpdate`, `removeLineItem`, `applyCartDiscount`, `addCartCodeDiscount`, `removeAllDiscounts`, `setCustomer`, `removeCustomer`, `addLineItemProperties`, `bulkAddLineItemProperties`, `removeLineItemProperties`, `setLineItemDiscount`, `bulkSetLineItemDiscounts`, `removeLineItemDiscount`, `addLineItemSellingPlan`, `removeLineItemSellingPlan`, `updateLineItemQuantity` |
| Vendor page | <https://shopify.dev/changelog/cart-mutations-reject-unconfirmed-writes-in-pos-ui-extensions-2026-10> |
| Review | Reviewed by a person, extracted by a model |

## Find it in your code

```sh
npx harbyn scan
```

This change names no identifier the scanner can match line by line, so the scan tells you whether your repository uses Shopify, from its packages and API hosts. Nothing leaves your machine.

## Sources

Where this event comes from: the page we read, when we read it, and the hash of that snapshot.

- <https://shopify.dev/changelog/feed.xml> (changelog, fetched 2026-10-07 23:09 UTC, sha256 `c7a9a174c5b3808940acc3e0f4125b7f8565241350f235213a9f30b710af5fca`)

## Related changes

### More from Shopify

- [POS UI extensions return percentage values for percentage discounts](https://harbyn.com/changes/shopify/2026-10-07-pos-ui-extensions-now-return-percentage-values-for-percentage-discounts.md) (Breaking change, announced Oct 7, 2026)
- [Product view events include currency](https://harbyn.com/changes/shopify/2026-10-08-hydrogen-developer-preview-update-october-8-2026.md) (Behavior change, announced Oct 8, 2026)
- [owner\_type required on metafield declarations in Checkout and Customer Account UI extensions from API version 2027-01](https://harbyn.com/changes/shopify/2026-10-08-new-owner-type-field-for-metafield-declarations-in-checkout-and-customer-acc-2.md) (Breaking change, announced Oct 8, 2026)
- [Global Catalog REST API stops serving traffic on November 2, 2026](https://harbyn.com/changes/shopify/2026-10-09-global-catalog-rest-api-stops-serving-traffic-on-november-2-2026.md) (Retirement, effective Nov 2, 2026)

### Changes at other vendors

- [Amazon Selling Partner API: October listing attribute usage and enumeration value updates](https://harbyn.com/changes/amazon-sp-api/2026-10-14-sp-api-updates-new-listings-items-api-ivp-values-in-eu5-jp-and-ca-stores-oct-2.md) (effective Oct 26, 2026)
- [Supabase: four CBC-mode TLS 1.2 cipher suites will be removed from project HTTP APIs](https://harbyn.com/changes/supabase/2026-10-12-an-outdated-subset-of-tls-1-2-ciphers-will-be-disabled-on-project-http-apis.md) (effective Nov 10, 2026)
- [Google Workspace APIs: OAuth clients must be marked as agentic to call Google Workspace MCP servers](https://harbyn.com/changes/google-workspace/2026-10-12-oauth-clients-must-be-marked-as-agentic-to-call-google-workspace-mcp-servers.md) (effective Nov 11, 2026)
- [Bitbucket Cloud API: Git Credential Manager upgrade required for OAuth 2.0 Git authentication](https://harbyn.com/changes/bitbucket/2026-10-13-git-credential-manager-upgrade-required-for-oauth-2-0-git-authentication.md) (effective Nov 30, 2026)

[All upcoming deadlines](https://harbyn.com/deadlines.md)