Starting with the GraphQL Storefront API 2026-01 release, the cartDiscountCodesUpdate mutation now requires the discountCodes argument to be explicitly included. Previously, developers could call this mutation without the discountCodes argument, though doing so would fail silently without actually modifying the cart.
This breaking change enforces stricter API validation and eliminates ambiguous mutation calls that appeared to succeed but produced no results. For Shopify developers building custom storefronts or headless commerce applications, this means any existing code calling cartDiscountCodesUpdate without the discountCodes field will now return an error rather than silently failing. The change improves code reliability by forcing developers to be intentional about discount code modifications and preventing accidental no-op mutations that could cause confusion during debugging.
cartDiscountCodesUpdate mutation calls and ensure the discountCodes argument is included in each callIf you're building apps that interact with Shopify's GraphQL Storefront API, GetShopifyToken provides secure, streamlined access token management so you can focus on implementing these API updates correctly rather than managing OAuth complexity.