You can register through the App Store where you also manage your subscription billing. Once App Store payment is chosen the billing for the subscription will be managed by the App Store (Google Play or Apple App Store) selected not by The Fitness App. 

Download My Fitness by Jillian Michaels App

Android - Google Play App Store

https://play.google.com/store/apps/details?id=com.emdigital.jillianmichaels&hl=en_US 

iOS - Apple App Store

https://itunes.apple.com/us/app/my-fitness-by-jillian-michaels/id1190148494