How to save an image on Android?

Hi! i'm new in unity and i'm trying to save an image for get it after. I try Application.CaptureScreenshot and the method with Texture2D.ReadPixel, i try to save in persistentDataPath (/data/user/0/my.package.name/files/), in /sdcard/Download/ and in /storage/emulated/0/Download. No method worked. In every manifest of my project i have WRITE_EXTERNAL_STORAGE permission. If i save to persistent data, i don't found it i found only cache of UnityAds, and if I save to Download folder I get access denied.

Anyone can help me?

Here's my code :

 Enumerator ScreenShot(){
         yield return new WaitForEndOfFrame ();
         Application.CaptureScreenshot ("ball.png");
         Application.CaptureScreenshot ("/sdcard/Download/ball.png");
 
 
 
         int width = Screen.width;
         int height = Screen.height;
         
 
         
         Texture2D tex = new Texture2D (width, height, TextureFormat.RGB24, false);
         
     
         
         tex.ReadPixels (new Rect (0, 0, width, height), 0, 0);
         
 
         
         tex.Apply ();
         
 
         
         byte[] bytes = tex.EncodeToJPG ();
         
 
         
         
         File.WriteAllBytes ("sdcard/Download/ball.png", bytes);
         File.WriteAllBytes (Application.persistentDataPath + "/ball.png", bytes);
 }

Before i check if folders exist : if(!System.IO.Directory.Exists("/sdcard/Download/")){ System.IO.Directory.CreateDirectory ("/sdcard/Download/"); }

         if(!System.IO.Directory.Exists(Application.persistentDataPath)){
             System.IO.Directory.CreateDirectory (Application.persistentDataPath);
         }

And i start IEnumerator with:

StartCoroutine(ScreenShot());

What I'm doing wrong?