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Hooktheory II examples not sounding - iPhone

Recently downloaded the update to Hooktheory II
which works perfectly on my IPad , but I get no sound when I play on my IPhone (11 Pro Max.)
I don’t see any settings location or a way to turn on or off and the sound works on all my other apps.
I’ve thus far haven’t found anything on the Forum.

Any thoughts on what to do? I’m at a loss.