Unauthorized MongoDB User: Not Authorized to Execute ‘find’ Command on ‘admin’ Database

Question

In my flutter app, using the file picker, I am trying to upload the file in the mongodb database with nodejs.

The following is the function that i used to send the file to the nodejs backend

void uploadFile(PlatformFile file) async {
  var request = http.MultipartRequest('POST',
      Uri.parse('$serverURL/files/upload'));
  request.files.add(http.MultipartFile.fromBytes(
    'file',
    File(file.path!).readAsBytesSync(),
    filename: file.name,
    contentType: MediaType('application', 'pdf'),
  ));
  var response = await request.send();
  if (response.statusCode == 200) {
    print("File uploaded");
  } else {
    print("File upload failed");
  }
}

I'm connecting with the mongoose database using the connect method

mongoose
  .connect(urlApp)
  .then(() => server.listen(process.env.PORT || 3000))
  .then(() => console.log("Server connected and database is also connected"))
  .catch((err) => console.error(err));

Here comes the actual logic of uploading the file

const conn = mongoose.connection;

let gfs;
conn.once("open", () => {
  gfs = Grid(conn.db, mongoose.mongo);
  gfs.collection("uploads");
});

const urlFile =
  "mongodb+srv://<userID>:<password>@docpatientclusteru.lpfrgin.mongodb.net/?retryWrites=true&w=majority";

const storage = GridFsStorage({
  url: urlFile,
  options: { useNewUrlParser: true, useUnifiedTopology: true },
  file: (req, file) => {
    return new Promise((resolve, reject) => {
      const filename = file.originalname;
      const fileInfo = {
        filename: filename,
        bucketName: "uploads",
      };
      resolve(fileInfo);
    });
  },
});

const upload = multer({ storage });

router.post("/upload", upload.single("file"), uploadFile);

whenever i try to call the uploadFile function the flutter app, i get the following error in my nodejs server.

MongoError: (Unauthorized) not authorized on admin to execute command { find: "fs.files", filter: { _id: ObjectID("659b2c1d5e73395e24d9ce58") }, limit: 1, singleBatch: true, batchSize: 1 }
at MongoError.create (C:\Users\Nadoshi\Desktop\yimbs development\Doc Patient App\backend\node_modules\mongodb-core\lib\error.js:31:11)
at queryCallback (C:\Users\Nadoshi\Desktop\yimbs development\Doc Patient App\backend\node_modules\mongodb-core\lib\cursor.js:212:36)
at C:\Users\Nadoshi\Desktop\yimbs development\Doc Patient App\backend\node_modules\mongodb-core\lib\connection\pool.js:469:18
at process.processTicksAndRejections (node:internal/process/task_queues:77:11)

I tried changing the built-in role from "read and write to any database" to "atlas admin", but the error remained.