Second attempt
I tried this app a while back and it didn’t work for me. Trying it today I still cannot adjust the tempo. On the tempo number in the middle of the phone screen it’s locked at 60 bpm. On the Apple Watch when attempting to adjust the tempo (still 60 bpm) via the crown it brings up the pricing for the app. I can initiate the tempo on both the phone and watch but neither will respond to anything else. Seems broken behind a pay wall.