Xamarin.Mac OS X App File.WriteAllText error

Question

I'm trying to save some data in a text file and then read it in macOS app. It works fine when I run it through debugger. But when I try to run it on another machine it gives an error.

"Access denied to path"

here's my code:

if (File.Exists(fileName))
            {
            using (FileStream aFile = new FileStream(Path.Combine(Directory.GetCurrentDirectory(), fileName), FileMode.Append, FileAccess.Write))//
                {
                    using (StreamWriter sw = new StreamWriter(aFile))
                    {
                        sw.WriteLine(fileData);
                    }
                }
            }
            else
            {
            using (StreamWriter sw = new StreamWriter(Path.Combine(Directory.GetCurrentDirectory(), fileName)))
                {
                    sw.WriteLine(fileData);
                }



            }

this code works fine on windows but why I have this error on mac?

I'm searching for a solution for two days. this question seems to be like mine but I'm having problem after creating the solution.

Xamarin IDE Access to the Path is denied

Note: I have run several tests and it seems my app don't have permissions on its own resource file that resides in the same directory.

So, my question is: Is there something wrong with my code (I'm new to macOS) or I need to do something else so that my app can write data to the file without showing that error?

I don't want to have admin rights to write to one file only.