Invalid request payload input on flutter post request - flutter

Question

I am trying to uploading multiple files from my flutter mobile app. Here is my screenshot of the postman. This works fine on postMan. But I am getting 400 errors on the flutter mobile app. I can't find out where is the problem?
Now here is the code of my flutter mobile app upload.
if(images.length>0){
for (int i = 0; i < images.length; i++) {
var path = await FlutterAbsolutePath.getAbsolutePath(images[i].identifier);
String fileName = path.split('/').last;
var file = await MultipartFile.fromFile(path, filename:fileName);
multipart.add(file);
}
FormData imageFormData = FormData.fromMap(
{
"feedId": value.id,
"images": multipart,
"userInformationsId": value.userInformationId
});
print(multipart.length);
uploadFeedPicture(imageFormData);
}
Future<String> uploadFeedPicture(FormData _imageformData) async{
String at = await _apiProvider.getAccessToken();
Dio dio = new Dio();
// dio.options.headers['accept'] = 'application/json';
// dio.options.headers["content-Type"] = "multipart/form-data";
dio.options.headers["Authorization"] = "Bearer ${at}";
dio.options.baseUrl = getBaseUrl();
var _baseUrl = getBaseUrl();
await dio.post('/api/feed/upload', data: _imageformData, options: Options(
followRedirects: false,
validateStatus: (status) { return status < 500; }
), onSendProgress: (int sent, int total) {
print("$sent $total");
},).then((value) {
print(value.data);
print(value.headers);
}
).catchError((error) => print(error) );
}
And I am getting this response.
{statusCode: 400, error: Bad Request, message: Invalid request payload input}
Please Help me out where is the problem? I try with change content-type but not working.

Answer 1

After trying so many different ways I found the solution. Here it is.
if(value.id != null){
String at = await _apiProvider.getAccessToken();
Map<String, String> headers = { "Authorization": "Bearer ${at}"};
var uri = Uri.parse('$baseUrl/api/feed/upload');
var request = http.MultipartRequest('POST', uri);
request.headers.addAll(headers);
if(images.length>0){
for (int i = 0; i < images.length; i++) {
var path = await FlutterAbsolutePath.getAbsolutePath(images[i].identifier);
// String fileName = path.split('/').last;
var file = await MultipartFile.fromPath("images",path);
request.files.add(file);
}
request..fields['feedId'] = value.id;
request..fields['userInformationsId'] = value.userInformationId;
var response = await request.send();
if (response.statusCode == 200) {
Navigator.pop(context);
showSuccessToast("Posted succesfull");
counter.update(0);
Navigator.push(
context,
MaterialPageRoute(builder: (context) => HomePage()),
);
}else{
showErrorToast("Upload image failed");
}
}
}