Register custom database pricing

Register your own managed database rates, keyed by engine, edition, deployment option, storage type and instance type alongside the usual provider, service and region. An entry is upserted on the full natural key (provider, service, region, availability zone, usage type, engine, edition, deployment option, billing config, storage type, instance type, architecture and period billing hours), so re-posting with a new cost keeps its id; changing any key field mints a new one. The returned id is what you attach with the costgraph.ai/pricing-id.database label or tag. Superseded by POST /v1/marketplace/databases, which returns RFC 9457 problem responses on failure.