Amount charged each cycle (decimal-string amount + currency). Required.
Billing interval unit, e.g. "day", "week", "month". Required.
Number of interval units per cycle (e.g. interval="month", intervalCount=3 → quarterly). Required.
Your unique plan reference. Required.
Human-readable plan name. Required.
Total number of cycles to bill before the plan completes. Required.
Parameters for creating a recurring billing plan (the reusable template a subscription is based on).