How to play a a sound from the app resources folder on button press, with AudioKit? - audiokit

Question

I I'm trying to play a random sound from the app resources folder in an iOS app.
I am using AudioKit v5 v5-main branch, and Swift 5.3 on XCode 12. The app builds but crashes when I press the play button in the UI; the error is listed below the code:
class ViewController: UIViewController {
...
// For audio playback
let engine = AudioEngine()
let player = AudioPlayer()
let mixer = Mixer()
override func viewDidLoad() {
super.viewDidLoad()
...
// Initialize AudioKit pipeline
mixer.addInput(player)
engine.output = mixer
do {
try engine.start()
} catch let err {
print(err)
}
}
#IBAction func playButton(_ sender: UIButton) {
playSound()
}
func playSound() {
let randomSound = sounds.randomElement()
let url = Bundle.main.url(forResource: randomSound, withExtension: "wav")
print("URL: \(url)")
// player = try! AVAudioPlayer(contentsOf: url!)
player.scheduleFile(url!, at: nil)
player.play()
}
}
The error produced when the button is pressed is:
*** Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason: 'required condition is false: _outputFormat.channelCount == buffer.format.channelCount'
terminating with uncaught exception of type NSException
(lldb)
I believe that I may be failing to initialize the audio engine properly, but I'm not sure how/where to do that. Any pointers?