So you promised a 1 month free trial, and after one month you either disable the app, or not charge and let them continue their free trial. Either is allowed or makes sense.
The developers can't choose to not charge or to cancel a subscription. The user must cancel. The devs cannot refund a subscription that a user forgot to cancel.
Does Apple now allow an app to start up but do nothing? Back when I was a developer, that was against the AppStore guidelines.