Subscription Start-Date Override (Platform + API)

Problem Statement

Administrators need the ability to set or backdate the subscription start date directly from the platform. The current platform does not provide a controlled way to adjust start_date, creating gaps when aligning entitlement periods or correcting subscription timelines.
The feature must also be supported through the Subscription Create API endpoint, ensuring API-first consistency.

User Story

As an admin or integrator, I want to explicitly set the subscription start date (including backdating) via the platform UI and the Subscription Create API, so that subscription timelines can be accurately initialized without relying on workarounds.

Definition of Done (DoD)

1. Functional Requirements

• The platform allows administrators to set or backdate the subscription start_date.

• The Subscription Create API accepts an optional start_date parameter.

• Changing the start date does not modify:

  • Invoice start date

  • Invoice line-item periods

  • Historical invoice data

2. Renewal Logic

• Renewal date is based on the subscription's start date, including backdated values.
  Example: Backdating to Aug 1 → next renewal occurs Aug 1 of the next cycle.

3. Guardrails

• Start-date modification (UI or API) allowed only when:

  • The subscription is not set to auto-renew, and

  • No renewal phase or future renewal event is scheduled.

• Operation must be blocked when renewal logic depends on the existing start date.

4. Scope

• Applies to all plan types (shipment-based and time-based).

• Implemented in:

  • Platform UI (admin-level controls)

  • Subscription Create API

5. UI Note

• Where applicable, the UI must clearly state:
  “Start date modifications do not affect invoice dates.”