When i use iOS auto-renewal subscriptions, is there a way to check if a user doesn't have an active payment method, or do I need to wait a month for Apple to attempt the renewal?
It's not up to you to be able to be the checker of such things, that lies within Apple's domain. They don't expose any methods for you to make any such checks. They attempt to renew when a subscription is due, and you're not allowed to add a subscription without the user providing input. Further, existing subscriptions are managed outside your app within Settings.