Save Data Android C#

Hello i write a Script to Save data for my Android Game . On my Pc all worked. But on Android not if i win and the game want to Save nothing happends and it dont go on. Code

 public void SaveData()
     {
         bool nextlevel = true;
 
         if (!Directory.Exists("Saves"))
             Directory.CreateDirectory("Saves");
 
         BinaryFormatter formatter = new BinaryFormatter();
         FileStream saveFile = File.Create("Saves/save.level." + nextScence);
 
         formatter.Serialize(saveFile, nextlevel);
         saveFile.Close();
     }

Thanks for help ( Iam German)