How do I stop paying for a app

If you have a recurring payment for an app, it is more than likely a subscription. You would need to manage and cancel that subscription. See the instructions here, View, change, or cancel your subscriptions - Apple Support

Start here: View, change, or cancel your subscriptions - Apple Support

Hi!

If this is a subscription, go to Settings > iTunes and App Store > Your Apple ID > Subscriptions. Select subscription and touch Cancel Subscribe.