What’s the difference between a paid app and an in-app purchase?

Medisafe is a free app —  you can go to Google Play or the App Store and download and use it for free. So-called  “paid apps” require you to pay up to $59.99 to download before you can use them at all.
Medisafe now has in-app purchases that don’t affect the free version at all, but allow premium members to have unlimited access to Medfriends, measurements, dependents, no banner ads, change their theme colors and more.