Subscription — Overview

Subscription handles long-term enrollment and recurring billing: customers enroll in a "package" (subscription), the system creates period-based billing schedules, issues invoices, and manages class booking, add-ons, and discounts per period.

Quick picture

Think of a learning center selling a "term package":

1. Admin creates a Subscription (package): name, price, schedule, booking conditions.
2. Customer / admin enrolls a student → creates an Enrollment.
3. System builds a BillingSchedule (billing periods, each with an amount).
4. On schedule, each period creates an Invoice; admin can schedule / approve / skip.
5. During the process: add add-ons, apply discounts per period; optionally skip a period.

Two Subscription types

Type	Subscription.TypeId	Meaning
BookingAndBilling (default)	null/0	Books class places and collects money; requires SubscriptionProduct (Program) setup.
BillingOnly	1	Recurring billing only; skips booking-product validation, hides Program section.

Main "objects"

Name	One sentence
Subscription	Package/template: price, schedule, booking conditions.
Enrollment	Runtime enrollment, with Submitted→Approved→Confirmed lifecycle.
BillingSchedule	Period-based billing schedule; canonical source for booking period selection.
Invoice	Invoice per period, with financial status lifecycle.
Add-on / Discount	Extra service / discount applied per booked period.
Term	Academic period; subscription links to term.

Suggested reading order

1. End-user view — what admin and customer do.
2. Core concepts — Subscription vs Enrollment, billing, booking.
3. Architecture & data — tables and relationships.
4. Codebase flow — API, service, validation.
5. Data & read/write tables — what Term is, tables by flow.
6. Common cases — skip, add-on, double-booking, etc.