Sharing a text file (csv) with share_plus: "unable to attach file" - flutter

Question

I want to get data from Firestore, convert it into csv format, then share it using the user's method of choice (e.g. email). I'm using the csv package to convert the data to csv, the path_provider to get the directory to write the file to the phone, and the share_plus package to share the file.
However, when I tap a share method (e.g. Gmail, Outlook, Whatsapp), it opens the right app but then I get a message on the phone like "Unable to attach file" (but there is no error in my app). The file is definitely being written as I can read it and it comes back with the expected string. The ShareResultStatus that is returned by the share is 'successful' Can anyone figure it out what the problem is and how to fix it?
Here is my code:
Future exportData() async {
// Dummy data (in reality, this will come from Firestore)
List<List> dummyData = [
['Date', 'Piece', 'Rating'],
[DateTime.utc(2022, 05, 01), 'Sonata', 4],
[DateTime.utc(2022, 05, 02), 'Sonata', 2],
];
// Turn into CSV
String csvData = _convertToCsv(dummyData);
// Write to local disk
await _writeData(csvData);
// Share
String filePath = await _filePath;
final result =
await Share.shareFilesWithResult([filePath], mimeTypes: ['text/csv']);
print(result.status);
}
And here are the functions used in above code:
Future<String> get _filePath async {
final directory = await getApplicationDocumentsDirectory();
return '${directory.path}/my_practice_diary_data.csv';
}
Future<File> _writeData(String csvData) async {
String filePath = await _filePath;
final file = File(filePath);
return file.writeAsString(csvData);
}
String _convertToCsv(List<List> data) {
String result = const ListToCsvConverter().convert(data);
return result;
}
Note: I've tried doing it both as txt and csv files, got same result
*** EDIT (06/06/2022): After a lot of reading and watching youtube videos, I have come to realise that the problem is that the directory getApplicationDocumentsDirectory() is only accessible by my app (and hence the app that is is being shared to, like gmail, cannot read it).
For now I have worked around it by using the package mailer and using user's google credentials to send emails (I followed these helpful youtube tutorials: Flutter Tutorial - How To Send Email In Background [2021] Without Backend and Flutter Tutorial - Google SignIn [2021] With Firebase Auth - Android, iOS, Flutter Web.
However, it would still be nice to know a nice way to generate a file and share it using share_plus, as per my original question. I believe that this can be achieved via one of two ways:
Find a way to allow other apps to access this specific file in the app directory; or
Find a way to download the file into an external storage (like downloads folder), then share that. (I cannot find a way to do this on both Android and iOS).
Anyone who knows how to do these or any other solution to the problem, please share!