Read-only preview of what POST .../change-cycle would actually charge/credit right now

GET 
/instances/:instanceId/billing/preview-cycle-change

Applies the exact same validation as the real change-cycle route (active subscription required, target cycle must differ, a real Stripe Price must exist) and never changes anything — backed by Stripe's own invoice-preview machinery, so the number can't drift from what actually happens on confirm. Meant to back a confirmation step before the customer commits to a switch.

Request

Responses

200

OK

400

Validation error

403

Valid credentials, but not authorized for this instance

409

No active subscription to change

501

Stripe not configured, or no real Stripe Price exists yet for the target cycle