Merges items from an anonymous Cart into the most recently modified active Cart of a Customer. If no active Cart exists, the anonymous Cart becomes the Customer's active Cart.
If the Cart exists in the Project but does not have a `store` specified, or the `store` field references a different Store, a [ResourceNotFound](ctp:api:type:ResourceNotFoundError) error is returned.
For more information about merge mode behaviors, merge rules, and tax recalculation, see [Merge a Cart](/../api/carts-orders-overview#merge-a-cart).
Merges items from an anonymous Cart into the most recently modified active Cart of a Customer. If no active Cart exists, the anonymous Cart becomes the Customer's active Cart.