Problem
I'm trying to record microphone data using AVAudioEngine. This is my setup.

First I create singleton session, set sessions category and activate it.

    let audioSession = AVAudioSession.sharedInstance()
    
    do {
      try audioSession.setCategory(.record)
      try audioSession.setActive(true)
    } catch {
      ...
    }

After that i create input format for bus 0, connect input and output nodes and install tap on input node(also tried to tap output node)

let inputFormat = self.audioEngine.inputNode.inputFormat(forBus: 0)
self.audioEngine.connect(self.audioEngine.inputNode, to: self.audioEngine.outputNode, format: inputFormat)
    self.audioEngine.outputNode.installTap(onBus: 0, bufferSize: bufferSize, format: inputFormat) { (buffer, time) in
      let theLength = Int(buffer.frameLength)
      var samplesAsDoubles:[Double] = []
      
      for i in 0 ..< theLength
      {
          let theSample = Double((buffer.floatChannelData?.pointee[i])!)
          samplesAsDoubles.append( theSample )
      }
      ...
    }

All of the above is in one function. I also have another function called startRecording which contains the following.

    do {
      try audioEngine.start()
    } catch {
      ...
    }

I have also verified microphone permissions which are granted.

Start method fails and this is the response

The operation couldn’t be completed. (com.apple.coreaudio.avfaudio error -10875.)

Questions
Based on documentation there are three possible causes

- There’s a problem in the structure of the graph, such as the input can’t route to an output or to a recording tap through converter nodes.

- An AVAudioSession error occurs.

- The driver fails to start the hardware.
```

I don't believe it's the session one, because i set it up via documentation.

If the driver fails, how would i detect that and handle it?

If graph is setup incorrectly, where did i mess it up?