In the light version of SonoFlex for iOS, there is a limitation of 20 voice outputs. After that the app must be restarted to use the voice output feature again. In the full version of SonoFlex, there is no limitation.
How to restart the iPad:
1) Press and hold the Sleep/Wake button until a red slider appears.
2) Use the slider to turn the iPad off.
3) Pause a few moments while your iPad shuts down, then hold the Sleep/Wake button until the Apple logo appears.
4) When you see the Apple logo, release the Sleep/Wake button.