Screenshot fail to store in ios devices

I use Screenshot code that works perfectly on pc, but not on ios devices.

typically ios devices wii ask for permission to assess the photos library.

but it didn't?

public IEnumerator CaptureScreen()
    {
        yield return null;

        yield return new WaitForEndOfFrame();

        ScreenCapture.CaptureScreenshot(Application.persistentDataPath + $"/Screenshot.png");
    }

I also use fellow code,it;s no work

byte[] pngShot = ImageConversion.EncodeToPNG(tex_transparent);
System.IO.File.WriteAllBytes(Application.persistentDataPath + $"/Screenshot{index}.png", pngShot);