Swift AVAudioEngine not working as in Apple Documentation

Question

I am trying to build a simple mp3 player using AVAudioEngine.

I made one using AVAudioPlayer and it worked fine (eventually).

I now need to move up to AVAudioEngine to give more functionality and I cannot get it to play even a simple file.

I have used exactly the code described in the Apple Documentation

And although the app builds (in Playgrounds at present) and prints all the messages to the console that I put in to show progress, nothing can actually be heard.

Here is the code I am using. Most from the Apple notes, but some from other questions I found online.

func azAEngine () {
    let audioFile = try! AVAudioFile(forReading:URL(fileURLWithPath:Bundle.main.path(forResource:"bluesuedeshoes.mp3", ofType:      nil)!)))

    let azURL = URL(fileURLWithPath(Bundle.main.path(forResource:"bluesuedeshoes", ofType: "mp3")!))
    
    print(azURL)     
    let audioEngine = AVAudioEngine()    
    let playerNode = AVAudioPlayerNode()    
    
    // Attach the player node to the audio engine.
    audioEngine.attach(playerNode)
    print("Audioengine attached ")
    // Connect the player node to the output node.
    audioEngine.connect(playerNode,                         
                        to: audioEngine.outputNode, 
                        format: audioFile.processingFormat)
    print("playernode attached")
    playerNode.scheduleFile(audioFile, 
                            at: nil, 
                            completionCallbackType: .dataPlayedBack) { _ in
        print("Done")
        /* Handle any work that's necessary after playback. */
    }
    
    do {
        try audioEngine.start()
        playerNode.play()
        print("playernode here ")
    } catch {
        /* Handle the error. */
        print("Failed")
    }
    print("player started") 
}