How to post image to my server from Flutter?

Question

I have a small server based on node JS, which communicates with Post Gre SQL database, and server is working on port 5000. I have route called uploadImage, which uploads an image to the /uploads folder, and uses Bearer token for the authorization. I have not created this server in React, and don't know how to use headers correct in http.multiPartRequest to post image. Code for posting image is here:

const express = require('express');
const router = express.Router();
const pool = require("../database");
const config = require('../config/config');
const expressJwt = require('express-jwt');
const jwt = require('jsonwebtoken');
const multer = require('multer');
const moment = require('moment');

var storage = multer.diskStorage({
    destination: function (req, file, cb) {
        cb(null, 'uploads/')
    },
    filename: function (req, file, cb) {
        cb(null, moment().unix() + '_' + file.originalname);
    }
});

var upload = multer({ storage: storage });

router.route('/uploadImage').post(expressJwt({ secret: config.serverSecretKey }),upload.array("files"), async function (req, res) {
    let retVal = { msg: '', logoUrl: ''};

    try
    {
        if (req.user == null || req.user === undefined) {res.sendStatus(401); return;}
        if (req.user.accountid == null || req.user.accountid === undefined || !req.user.app) {res.sendStatus(401); return;}

        let files = req.files;
        if(files && files.length > 0 ){
            retVal.imageUrl = 'http://localhost:5000/uploads/' + files[0].filename;
        }else {
            retVal.msg = 'Error';
        }

        res.status(200).json(retVal);

    }catch(err){
        console.log({err});
        res.status(401);
    }
});

My client code is:

  onTapUploadImage() async {
    final imagePicker = ImagePicker();
    final image = await imagePicker.pickImage(source: ImageSource.gallery);
    if (image != null) {
      final File? imageFile = File(image.path);
      if (imageFile != null) {
        final SharedPreferences sharedPrefs =
            await SharedPreferences.getInstance();
        final String? token = await sharedPrefs.getString("token");
        final httprequest = await http.MultipartRequest('POST', Uri.parse('http://darivoje.ddns.net:5000/app-api/uploadImage'));
        httprequest.headers.addAll({HttpHeaders.authorizationHeader: 'Bearer $token'});
        httprequest.files.add(http.MultipartFile.fromString('picture', imageFile.path));
        final postreq = await httprequest.send();
      }
    } else {
      print('No image selected.');
    }
  }