I got this working by editing the line it refers to in the code of the SmartApp.
Line 165 reads:
if((device.currentSide == "Right" && foundationStatus.fsCurrentPositionPresetRight != "Flat") || (device.currentSide == "Left" && foundationStatus.fsCurrentPositionPresetLeft != "Flat")){
I fixed it by changing that to:
if((device.currentSide == "Right") || (device.currentSide == "Left")){
Basically, it just doesn’t look for the status of the bed’s foundation, and I’d imagine breaks that functionality (but I don’t have a foundation, so I’m imagining that’s where the error came in in the first place.