Application.persistentDataPath seems not to work on iOS

I am currently developing a game where the user can send an e-mail with an attachment (CREDITS TO Om Shridhar https://www.linkedin.com/pulse/code-send-e-mail-attachment-from-unity-c-using-smtp-om-shridhar). It works very well in the unity Editor but not on my iOS device. The player tabs a button to execute Takescreenshot(); and another one to SendMail(); The code is the following:

using System.Net; using System.Net.Mail; using System.Collections; using System.Net.Security; using System.Security.Cryptography.X509Certificates; using System.IO;

public class MailerScript : MonoBehaviour { string _sender = ""; string _password = "";

 public string ScreenshotName = "screenshot.png";
 private string screenShotPath;
 public MailerScript()
 {
     _sender = "here comes the sender mail";
     _password = "here comes the password";
 }

 public void Takescreenshot()
 {
     screenShotPath = Application.persistentDataPath + "/scrn-1.jpg";
     Texture2D tex = new Texture2D (Screen.width, Screen.height);
     tex.ReadPixels (new Rect(0, 0, Screen.width, Screen.height), 0, 0);
     tex.Apply ();
     var bytes = tex.EncodeToJPG();
     Destroy (tex);
     System.IO.File.WriteAllBytes(screenShotPath, bytes);
     //screenShotPath = Application.persistentDataPath + "/" + ScreenshotName;
     //if(File.Exists(screenShotPath)) File.Delete(screenShotPath);
     Application.CaptureScreenshot(ScreenshotName);
     Debug.Log ("TAKESCREENSHOT FUNCTION EXECUTED");
 }


 public void SendEmail()
 {
     Debug.Log ("SEND EMAIL FUNCTION EXECUTED");
     //For File Attachment, more files can also be attached
     Attachment att = new Attachment(screenShotPath);
     //tested only for files on local machine



     //Hardcoded recipient email and subject and body of the mail
     string recipient = "here comes the recipients mail";
     string subject = "Test Mail";
     string message = "Hello World";

     SmtpClient client = new SmtpClient("smtp.gmail.com");
     //SMTP server can be changed for gmail, yahoomail, etc., just google it up


     client.Port = 25;
     client.DeliveryMethod = SmtpDeliveryMethod.Network;
     client.UseDefaultCredentials = false;
     System.Net.NetworkCredential credentials = new System.Net.NetworkCredential(_sender, _password);
     client.EnableSsl = true;
     client.Credentials = (System.Net.ICredentialsByHost)credentials;

     try
     {
         var mail = new MailMessage(_sender.Trim(), recipient.Trim());
         mail.Subject = subject;
         mail.Body = message;
         mail.Attachments.Add(att);
         Debug.Log("Attachment is now Online");
         ServicePointManager.ServerCertificateValidationCallback = delegate(object s, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
         {
             return true;
         };

         client.Send(mail);
         Debug.Log("Success");
     }
     catch (Exception ex)
     {
         Debug.Log(ex.Message);
         throw ex;
     }
 }

}

I really checked the internet for possible solutions for hours but with no luck. I really appreciate every help on this! Best wishes and thank you in advance!