The app download is free. Only the Coach subscription will have a monthly fee involved. You'll find the pricing for your region in the app in the Coach tab before purchasing. The app pricing varies depending on the plan you choose (3/6/12 months).
If you don't want to use the Coach Features, just click the X on top left or right of the screen, then you can use the free version.
The app has a lot of free features, more than most other fasting apps:
+ Choose from 12 different fasting plans like 5-2 or 16-8
+ A fasting timer to track your fasting
+ Multiple notification options to stay on track with your fasting times
+ Track your weight and add notes
+ Detailed statistics on your weight progress, BMI and the way to your goal
+ A large knowledge library about fasting, eating periods and weight loss
You can try the free features first and then go for the more effective way of the Coach later.