Chapter 20 Apple Watch Haptic Feedback not working

I’ve followed the instructions in Chapter 20, Apple Watch, for Taptic Feedback, but it isn’t working properly on my iPhone (1st generation). It makes the sound, but not the taps. I’ve also tried running the project in the ‘final’ folder, with the same problem. My phone does produce taps and vibrations from other notifications. Any ideas how to fix this?