promotional_grant_no_metered_items
billing.promotional_credit.grant requested for a subscription carrying no metered items for the grant to apply to. A Stripe billing credit grant reaches metered subscription items only, so it cannot touch the class base fees, the $200 extra session, the $250 first receptionist connection or the $150 additional ones - the live case is a standalone receptionist, whose invoice is licensed fees only because no inbound leg emits a usage row (CANON 152 as corrected). Without this refusal the grant would report as issued and reduce nothing. What an operator does: use a credit note against the finalized invoice instead - comping a licensed fee is a credit note or it is nothing. P2, unbuilt.
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/promotional_grant_no_metered_items",
"title": "…",
"status": 409,
"detail": "…",
"instance": "/v1/…"
}