How to Play Audio File on Apple Watch Physical Speaker

I am writing a watchOS app where I have some audio files that I want to play at various points. I am using AVAudioPlayer. It all works in the simulator and it also works if I have Air Pods connected to my watch via Bluetooth. However I get no sound if there isn't a paired set of earphones. In the case of no earphones I would like the sounds to play from the physical watch speaker. I can't seem to find any documentation on how to cause that to happen.

Any hints or tips are appreciated.

How to Play Audio File on Apple Watch Physical Speaker
 
 
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