portal_subscription_update_unavailable
POST /v1/billing/customer-portal with flow="subscription_update" now directs all plan and connection changes to Vocapable Billing for quote review and confirmed purchase. A legacy dedicated editor configuration does not bypass purchase ownership. The request shape remains accepted, but no hosted subscription editor is opened. Payment management, invoices and cancellation use a freshly verified general configuration.
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/portal_subscription_update_unavailable",
"title": "…",
"status": 409,
"detail": "…",
"instance": "/v1/…"
}