First try different cables and exchange IN and OUT. If all else fails, check settings, especially:
[RCV CHANNEL] – try OMNI and see if it changes anything.
[RCV CTL] – you’ve probably used this.
I figured out what it was – I had a USB cable plugged in to change some settings in the H9 app, and apparently the pedal ignores din midi when a USB cable is plugged in? As soon as I remove the USB cable, everything started working as I would expect.