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 agrument to be included. Previously, the cartDiscountCodesUpdate mutation would accept a mutation with no discountCodes argument, which would not actually modify the cart in any way.

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