Every user that has reported this issue has had the master hardware volume switch on the side of the iPhone/iPad set to “off”. Can you double check to make sure that this is on when using the Hooktheory app (see image below) ?
We realize many video and music apps (iTunes, YouTube, Netflix, etc.) don’t mute their output based on the status of that switch. We are working on a fix so the audio from our app plays even when the master hardware with is set to off.
On newer iOS devices, the hardware switch has been removed and replaced by a software setting accessible by swiping up
There is a setting in Settings/Sounds which silences the typing and the lock sound. It is not that.
There is a bell symbol in the software switches (NOT at the top as an indicator icon to show an existing status) you can find by swiping up. It you tap it once it toggles on and off. This can cause a muting of the sound with Hooktheory I and Hooktheory II book/apps.
I’m having the exact same problem, but I’m on my iMac desktop computer. If I export my work to Logic Pro, I can hear it, but while it’s in HookTheory/Hookpad, I get no sound at all. It used to work. I don’t know what happened