animate a moving watermark over video using calayer - swift

Question

I am on swift and trying to make a watermark move positions over a video. so far all I'm getting is a watermark that stays still over the video that is playing. how can I make it move? Basically what I'm trying to replicate is like the watermark from tiktok videos that pop in from one location to the other. I am really confused as to why this doesn't work. please help. thanks!
func processVideoWithElements(item: MediaItem, completion: #escaping ProcessCompletionHandler) {
let mixComposition = AVMutableComposition()
let compositionVideoTrack = mixComposition.addMutableTrack(withMediaType: AVMediaType.video, preferredTrackID: kCMPersistentTrackID_Invalid)
let clipVideoTrack = item.sourceAsset.tracks(withMediaType: AVMediaType.video).first
let clipAudioTrack = item.sourceAsset.tracks(withMediaType: AVMediaType.audio).first
do {
try compositionVideoTrack?.insertTimeRange(CMTimeRangeMake(start: CMTime.zero, duration: item.sourceAsset.duration), of: clipVideoTrack!, at: CMTime.zero)
} catch {
completion(MediaProcessResult(processedUrl: nil, image: nil), error)
}
if (clipAudioTrack != nil) {
let compositionAudioTrack = mixComposition.addMutableTrack(withMediaType: AVMediaType.audio, preferredTrackID: kCMPersistentTrackID_Invalid)
do {
try compositionAudioTrack?.insertTimeRange(CMTimeRangeMake(start: CMTime.zero, duration: item.sourceAsset.duration), of: clipAudioTrack!, at: CMTime.zero)
} catch {
completion(MediaProcessResult(processedUrl: nil, image: nil), error)
}
}
compositionVideoTrack?.preferredTransform = (item.sourceAsset.tracks(withMediaType: AVMediaType.video).first?.preferredTransform)!
let sizeOfVideo = item.size
let optionalLayer = CALayer()
processAndAddElements(item: item, layer: optionalLayer)
optionalLayer.frame = CGRect(x: 0, y: 0, width: sizeOfVideo.width, height: sizeOfVideo.height)
optionalLayer.masksToBounds = true
// animate layer ---------------------------------------
let positionAnimation = CABasicAnimation(keyPath: #keyPath(CALayer.position))
positionAnimation.beginTime = CMTime.zero.seconds
positionAnimation.fromValue = CGPoint(x: -20, y: 100)
positionAnimation.toValue = CGPoint(x: 280, y: 100)
positionAnimation.duration = 3//item.sourceAsset.duration.seconds
positionAnimation.repeatCount = 2
positionAnimation.autoreverses = true
optionalLayer.add(positionAnimation, forKey: #keyPath(CALayer.position))
//------------------------------------
let parentLayer = CALayer()
let videoLayer = CALayer()
parentLayer.frame = CGRect(x: 0, y: 0, width: sizeOfVideo.width, height: sizeOfVideo.height)
videoLayer.frame = CGRect(x: 0, y: 0, width: sizeOfVideo.width, height: sizeOfVideo.height)
parentLayer.addSublayer(videoLayer)
parentLayer.addSublayer(optionalLayer)
let videoComposition = AVMutableVideoComposition()
videoComposition.frameDuration = CMTimeMake(value: kMediaContentTimeValue, timescale: kMediaContentTimeScale)
videoComposition.renderSize = sizeOfVideo
videoComposition.animationTool = AVVideoCompositionCoreAnimationTool(postProcessingAsVideoLayer: videoLayer, in: parentLayer)
let instruction = AVMutableVideoCompositionInstruction()
instruction.timeRange = CMTimeRangeMake(start: CMTime.zero, duration: mixComposition.duration)
let videoTrack = mixComposition.tracks(withMediaType: AVMediaType.video).first
let layerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: videoTrack!)
layerInstruction.setTransform(transform(avAsset: item.sourceAsset, scaleFactor: kMediaContentDefaultScale), at: CMTime.zero)
instruction.layerInstructions = [layerInstruction]
videoComposition.instructions = [instruction]
let processedUrl = processedMoviePath()
clearTemporaryData(url: processedUrl, completion: completion)
let exportSession = AVAssetExportSession(asset: mixComposition, presetName: AVAssetExportPresetHighestQuality)
exportSession?.videoComposition = videoComposition
exportSession?.outputURL = processedUrl
exportSession?.outputFileType = AVFileType.mp4
exportSession?.exportAsynchronously(completionHandler: {
if exportSession?.status == AVAssetExportSession.Status.completed {
completion(MediaProcessResult(processedUrl: processedUrl, image: nil), nil)
} else {
completion(MediaProcessResult(processedUrl: nil, image: nil), exportSession?.error)
}
})