Create a recurring billing plan (scope: subscriptions:write).
The plan definition; see CreatePlanParams.
Optional { idempotencyKey } — retrying with the same key + body replays the original.
The created plan record.
List all subscription plans (scope: subscriptions:read).
The raw { items, nextCursor } (nextCursor always null) of plan records.
Recurring billing plans — the reusable templates subscriptions are created from (scope:
subscriptions:*).