Mac OS 10.15.7, Finale 26.3, imac 2015 quad-core i5

I have an organ score where I'm running the top staff on the Great on channel 2, and the 2nd staff on channel 3 for the Swell. That's fine. But then the right hand needs to go to the Swell. I've created an Expression like this:

...and nothing happens.
I've tried working around this by putting the music into Layer 2 and then setting Layer 2 in the score manager to channel 3. This gives me SILENCE in the right hand, a silence that persisted even when I changed the layer back, until I reverted to a previous version of the file.
I can kludge the next measures by setting Swell to Great, but later I really need diapason sound in both hands and so need to have them both on 2 (and there is no Swell to Great on this organ). It would seem to me that channel change is purely a Finale thing, since Hauptwerk is responding fine to channels 1, 2 and 3. What am I missing/doing wrong here?