I recently had an issue where the keyboard clicks on my iPad stopped working. I checked the settings and the sounds were turned on correctly. Then I remembered my daughter had borrowed the iPad and changed the side hardware switch from “lock rotation” to “mute sounds”. I had since switched it back to “lock rotation”. To fix this problem, I changed the switch back to “mute sounds” and then I was able to turn the sound back on with the switch. Once the sound was on, I then changed back to “lock rotation”. Problem solved.