design_partner_conversion_notice_missing
An operator tried to end a Comped Period - stop the Design Partner Credit and convert the tenant to the Conversion Price - and either no §6.4 sixty-day notice is recorded for that tenant or the recorded send date is fewer than sixty days before the requested Conversion Date. Under legal/design-partner-addendum.md §6.4 the notice is a condition of the conversion rather than a courtesy: a late notice postpones the Conversion Date day-for-day and the credit continues until then, so converting earlier would breach the executed document. What an operator does: send the notice restating the Conversion Price, the Conversion Date and the thirty-day opt-out deadline; record it with billing.conversion_notice.record; and retry with a Conversion Date at least sixty days after the send date. P2, unbuilt - no worker reads a date off a commercial row and nothing sends this notice today, so it is a calendar entry for a human.
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/design_partner_conversion_notice_missing",
"title": "…",
"status": 409,
"detail": "…",
"instance": "/v1/…"
}