Is it possible to charge the user a one dollar fee for every 24 hours not using the app? It seems like this would be very valuable, most people who download exercise apps do not continue to use them on a daily basis and this system would inspire them to be consistent.
What happens if a user loses their phone for two days? What happens if the app crashes? What happens if the user changes the data/time on the device?
What happens if the user goes to the hospital and is unconscious for a week?
Using money as a cudgel seems a great way to risk rejection, I think, if for no other reason that Apple not wanting to field disputes, refunds, etc.
Best to find another way to encourage your users so they want to participate without being penalized/threatened for their own good. They're already under enough pressure...they don't need more.
