UWP - nas network access denied

Question

I want to read some text files with extensions of .txt, .rtf and .log from a nas in my uwp app.

I have followed the instructions on this link, but there is still a "network access denied" error.

This is my Package.appxmanifest file.

EDIT

1. I use a FolderPicker to let the user choose the folder containing the log files, then I add that folder to FutureAccessList with a token.
2. I use the token in 1. to retrieve the folder, then read all the files in it.

Here is the relevant code.

1. public async static void locateLogsFolder()
   {
       var folderPicker = new FolderPicker();
       folderPicker.FileTypeFilter.Add("*");
       folderPicker.SuggestedStartLocation = PickerLocationId.ComputerFolder;
   
       IStorageFolder folder = await folderPicker.PickSingleFolderAsync();
       if (folder != null)
       {
           // Add to MRU with metadata (For example, a string that represents the date)
           string mruToken = StorageApplicationPermissions.MostRecentlyUsedList.Add(folder);
   
           // Add to FA without metadata
           string faToken = StorageApplicationPermissions.FutureAccessList.Add(folder);
   
           // To open this worksheet file later
           ApplicationDataContainer localSettings = ApplicationData.Current.LocalSettings;
           localSettings.Values[logsFolderKey] = faToken;
   
           loadData();
       }
       else
       {
           // The file picker was dismissed with no file selected to save
       }
   }
   

   2.

   private static async Task<bool> loadLogFiles()
   {
       ApplicationDataContainer localSettings = ApplicationData.Current.LocalSettings;
       if (localSettings.Values.ContainsKey(logsFolderKey))
       {
           string logsFolderPath = localSettings.Values[logsFolderKey].ToString();
           IStorageFolder logsFolder = await StorageApplicationPermissions.FutureAccessList.GetFolderAsync(logsFolderPath);
           logFiles = await logsFolder.GetFilesAsync();
           return true;
       }
       else
       {
           string message = "Logs folder has not been loaded successfully. \n"
                          + "Please locate the logs folder via the button on the upper left corner.";
           Utils.showMessage(message);
           return false;
       }
   }
   

Besides, I can get the names of the log files, and when I want to read the contents of them, the error network access denied occurred.

NAS device information: QNAP TS-231P

Any suggestions are welcome, and I can surely provide more details if needed.

Besides, I am looking for a free nas server that I can upload an small sample to test my app, but I fail to find one. I would like to know where I can find it. I am also not sure whether I can ask this on stackoverflow. If it is inappropriate, please direct me where I can post it instead, thanks.