How to know when a subscriptions ends

Hi, I am using spark to build my application. I already configured it. But I don't find how spark knows:

• When a subscription ends? In the subscriptions table, there is a ends_at field, but it is only populated when a user cancel his subscription.

• When a billing charge failed, I know that stripe handle subscription charges, but if it fails, how my app knows? I read the events on the docs, there is not such a event as SubscriptionChargeFailed or similar

• When a plan is near to expired. I want to send some emails and show notifications to the user to warning him

Thanks in advanced. I appreciate any help.