Midi is like telephone lines, both people have to be on the same line to communicate.
I set both keyboard and Harmonizer on channel five. Channel was for my left hand. It is the best if you want the unit to sing what you are fingering. But it is the most involved. There were times when a midi file changed my sending channel, that stopped all communication.

I like Gary’s and Don’s --- set it up and leave it alone. KISS
John C.