Write an open invoice off as bad debt, moving it to uncollectible. This is terminal: an uncollectible invoice cannot be paid, voided or credited afterwards.
The invoice's line items are deleted in the same transaction and their ledger journal entries are released back to the uninvoiced pool, so the response always carries an empty line_items array.
A credit note can never be written off, 409: it is allocated to the invoice it credits on creation, so its status is fixed.
Invoicing is opt-in per organization: unless the invoicing feature flag is enabled for your organization this endpoint returns 403.
The invoice cannot move to uncollectible from its current status. Only an open invoice can be written off.
Invoicing is not enabled for the organization, or the caller is missing the invoices:mark_uncollectible permission.
No such invoice, or the caller's user group does not grant access to its policy.
The invoice's linked payment has already gone to the bank and can no longer be cancelled (reconcile the payment first), the invoice is a credit note, or the invoice was modified by a concurrent writer.