⚠️ Beta Notice: This endpoint is currently in beta and may change or be deprecated at any time without notice.

Marks an existing sale as cancelled on the specified sales channel. Use this endpoint when a customer cancels their order, the store is unable to fulfil it, or the sale was created in error. Supply a cancellationReason from the documented enum and, optionally, a free-text cancellationNotes value (max 255 characters) to record additional context for reporting and audit. Cancellation is final: a cancelled sale cannot be reactivated, so submit a new sale if the customer reorders.