Writes the adjustment header, its lines and the resulting payment schedules, and submits them, in one transaction. Any failure rolls all of it back, so the call either succeeds completely or leaves nothing behind and can be sent again unchanged.

Returns the new adjustment id, not the adjustment - read the detail back with the GET. Reusing an externalId is refused with 409 and never alters the adjustment that already exists; its id is returned so it can be retrieved.

Which line fields apply depends on creditType: Against Invoice lines name the invoice line they credit and take the payment period from it, On Account lines carry a payDate and the payment period themselves. Each field says when it applies.