NO SOUND ON iOS VERSION?
Only versions prior to 7.4.0 have that problem.
The obvious solution is to update Mapping Tonal Harmony Pro iOS to the latest version
Just in case you don’t want to do that for some reason here’s the solution without updating the app:
Please make sure you iPad or iPhone are not muted (bell icon on the iPad, physical mute on the iPhone) or in “DO NOT DISTURB” mode (moon icon)
Here’s a screenshot of how it should look like: