By default the H9 isn't configured to send MIDI messages thru. So, you'll need to configure the first H9 to thru mode. You can do this in H9 Control by clicking on the Pedal button in the bottom menubar, going to MIDI Settings and then MIDI Output Mode, and selecting "Thru". You can do this directly on the H9 as well; please consult the user manual for instructions if you'd like to adjust it directly on the H9.