With the 2025-10 API version, the permitsSkuSharing argument has been updated for both the fulfillmentServiceCreate mutation and the FulfillmentService#create REST endpoint to return an error if a false value is passed in. Non-SKU sharing fulfillment services have been deprecated, and this pushes us in the direction of making all Fulfillment Services Sku sharing enabled.
This is a companion discussion topic for the original entry at https://shopify.dev/changelog/setting-permitsskusharing-argument-to-false-when-creating-a-fulfillment-service-returns-an-error