Orb Subscription API
A [subscription](/core-concepts#subscription) represents the purchase of a plan by a customer. By default, subscriptions begin on the day that they're created and renew automatically for each billing cycle at the cadence that's configured in the plan definition. Subscriptions also default to **beginning of month alignment**, which means the first invoice issued for the subscription will have pro-rated charges between the `start_date` and the first of the following month. Subsequent billing periods will always start and end on a month boundary (e.g. subsequent month starts for monthly billing). Depending on the plan configuration, any _flat_ recurring fees will be billed either at the beginning (in-advance) or end (in-arrears) of each billing cycle. Plans default to **in-advance billing**. Usage-based fees are billed in arrears as usage is accumulated. In the normal course of events, you can expect an invoice to contain usage-based charges for the previous period, and a recurring fee for the following period.