The cartDiscountCodeUpdate mutation now requires the discountCodes field

As part of the GraphQL Storefront API 2026-01 release, the cartDiscountCodesUpdate mutation now requires the discountCodes argument to be included. Previously, mutation calls without the discountCodes argument were allowed, but would not actually modify the cart in any way.

For more information about the Cart object and its related mutations, visit Shopify.dev.