New FREE_GIFT_CARD_NOT_ALLOWED error code for subscription billing attempts

We’ve added a new error code, FREE_GIFT_CARD_NOT_ALLOWED, to the SubscriptionBillingAttemptErrorCode enum. This error occurs when a subscription contract includes a gift card product with a purchase price of $0, which is not permitted under Shopify’s business rules.

While the situation is rare, this error can occur due to edge cases in dynamic pricing scenarios (for example, bundles or cart transformations could inadvertently set a gift card’s price to zero when part of a subscription contract). Previously, this resulted in a generic error message, making the cause difficult to troubleshoot.

Note: This error concerns the purchase price of the gift card as a product, not the monetary value loaded onto the card for the gift recipient.

Adding this specific error code improves clarity for Partners and developers, making it easier to diagnose and resolve issues related to subscriptions containing zero-priced gift cards.

This error code has been added to API versions 2025-01 and later.