issue while taking photo wtth flash On using AVCapturePhotoOutput

I am working on camera app. i am using AVCapturePhotoOutput for ios 10.x device and AVCaptureStillImageOutput for below 10.x devices.

I am using below capture settings while capturing Photo

let settings = AVCapturePhotoSettings()

let previewPixelType = settings.availablePreviewPhotoPixelFormatTypes.first!
        let previewFormat = [kCVPixelBufferPixelFormatTypeKey as String: previewPixelType,
                             kCVPixelBufferWidthKey as String: 1080,
                             kCVPixelBufferHeightKey as String: 1080,
                             ]
settings.previewPhotoFormat = previewFormat
settings.isHighResolutionPhotoEnabled = true
settings.flashMode = .on
settings.isAutoStillImageStabilizationEnabled = true
self.captureOutputPhoto?.capturePhoto(with: settings, delegate: self)

when i am try to capture photo using above setting

captureOutput:didFinishProcessingPhotoSampleBuffer:previewPhotoSampleBuffer:resolvedSettings:bracketSettings:error

above delegate throws error first time. I am beginner for AVCapturePhotoSettings. the problem is occurs after every successful photo capture with flash mode.