deferred_balance_insufficient
The same route when the tenant's remaining deferred-revenue balance (sum(deposits) - sum(settlements)) does not cover the invoice's amount_remaining in full. Settlement is all-or-nothing (ADR-0035 d4): paid_out_of_band pays the whole invoice and cannot part-pay, so the ledger never recognizes more revenue than cash was received and never partially backs an invoice it cannot fully cover - which is what makes over-recognition structurally impossible. Nothing was reserved or settled. What an operator does: record a deposit that covers it, or leave the invoice open under send_invoice - a near-exhausted deposit is a renewal decision surfaced by the revenue board's deferred-revenue disclosure, not a thing to force. P1 - built 2026-08-29 (ADR-0035 d4/d7).
Problem shape
Every non-2xx response is an RFC 9457 application/problem+json body. The type URI below is stable and machine-matchable, so branch on the final path segment (the code) and treat the status as redundant confirmation. See the error-handling guide.
{
"type": "https://docs.vocapable.com/errors/deferred_balance_insufficient",
"title": "…",
"status": 409,
"detail": "…",
"instance": "/v1/…"
}