func stopRingtone() {
    // 1. Stop the audio player
    audioPlayer?.stop()
    audioPlayer = nil
    
    // 2. Stop vibration
    vibrateTimer?.invalidate()
    vibrateTimer = nil
    
    // 3. Resume audio
    // This hands control back to the SDK to resume the video chat audio
    _ = startCapture()
    _ = startRendering()
    
    // ...
}