Start subscription grace period [Early Access]

Please note that this an Early Access phase. <br><br> Use this endpoint to notify Cleeng when an externally-managed subscription (EMS) enters a grace period (a temporary state where a payment attempt has failed, but the customer retains access while the external billing system retries the charge). <br><br> This call registers the grace period's start and its anticipated end date (gracePeriodEndDate) in the subscription history to ensure a reliable audit trail. Whenever you retrieve subscription data and a subscription is in grace period, gracePeriodEndDate is returned with date, otherwise it is null. <br><br> Note that this is a logging action; the endpoint does not alter the active subscription status itself, and the customer retains full access during this window.