Duo won't record both channels in Garageband

[mrs.emily.dunbar]

I want to record vocal via mic and guitar via 1/4 inch through the Duo in Garageband--and eventually 2 vocals with 2 mics. An error box tells me the channel I've selected is already in use. I thought this was the point of the Duo. Is there something obvious I'm missing? I'd appreciate any guidance. Thanks!

[mrs.emily.dunbar]

I FIGURED IT OUT. It was a simple matter of setting the channels for each track (pressing the red record button on each track and selecting channel 1 or channel 2). I figured it had to be something stupid easy. And it was. I figured I'd respond to my own post in case someone else was having plug-and-play frustrations.