422
payments.invalid_reasonpaymentsA reason is required for this action
Returned by the implementation; no specification rule declares it yet.
Some actions record why they were taken — a refund approval, a rejection — and the reason is part of the audit trail, not a courtesy. errors[0].field is reason.
Why the API refuses
a reason is required
What to do
Send a non-empty reason that a person reading the audit log in six months could act on. "ok" is technically accepted and practically useless; the operations team reading a disputed refund will be reading exactly this string.