Are there any ongoing fees?
There are no monthly fees, but if you want to continue to update your app after the first year there is a $99 yearly maintenance fee. Your app will continue to function, and will remain in the AppStore/Google Store even if you do not choose to continue with maintenance.
If you want to make an update or change your app after the first year, you will have to purchase the yearly maintenance.
The maintenance fee also helps maintain the app compatibility with future IOS/Android operating system releases.