Payments on Breath Hub are managed by the app stores (Apple App Store for iPhones, Google Play Store for Android phones) and your invoices are sent to you automatically by your app store.
How do I purchase a Breath Hub subscription?
To purchase a Breath Hub subscription, at first install, you can choose one of the available packages. Upon expiration of your subscription, the app will automatically prompt you to the subscription page when you try to play an audio session that requires a subscription. You can manage your subscriptions from Profile > Subscription > Manage subscription on the app, or from your phone’s app store.