Newbie question about Pianoteq/Mainstage

Hi all. Brand new to the forum, brand-new Pianoteq user.

I purchased Pianoteq so that my CPU load would be lower in Mainstage for my live gigs (and because I LOVE the expressiveness). But I'm having a little problem.

I'm able to insert Pianoteq in a Mainstage channel strip as an Audio Unit, but Pianoteq doesn't seem to be receiving MIDI messages from Mainstage. I play the keyboard, and there's MIDI activity, but no sound.

When I open the Pianoteq window and run my mouse across the keyboard at the bottom, I get sound. So that tells me Pianoteq is set up in the Mainstage signal chain on the audio side, but the two don't seem to be talking to each other on the MIDI side.

I've tried looking at the Options --> MIDI window, but it's looking Greek to me.

Can anybody help me get up and running?

Thanks in advance!