Flutter – Send a Map<String,double> to value of FormData in dio

I am trying to send a register request to the API with Dio, but when I use this code, the location field has a problem:

class RegisterRemoteDataSourceImpl extends RegisterRemoteDataSource {
  final Dio dio;
  final String username, email, password, confirmPassword;
  final String fullname, biography;
  final LocationEntity location;
  final File? profilePicture;

  RegisterRemoteDataSourceImpl({
    required this.dio,
    required this.username,
    required this.email,
    required this.password,
    required this.confirmPassword,
    required this.fullname,
    required this.biography,
    required this.location,
    this.profilePicture,
  });

  @override
  Future<bool> register() async {
    final formData = FormData.fromMap(
      {
        "username": username,
        "email": email,
        "password": password,
        "confirm_password": confirmPassword,
        "fullname": fullname,
        "biography": biography,
        "location": jsonEncode(location.toJson() /* {"latitude": 1234.0, "longitude": 1234.0}) */,
        "profile_picture": profilePicture == null
            ? null
            : await MultipartFile.fromFile(profilePicture!.path),
      },
    );
    final response = await dio.post(
      kApiRegister,
      data: formData,
    );

    if (response.statusCode == 200) {
      return true;
    } else {
      throw (response.statusMessage!);
    }
  }
}

The result I expect when I’m checking the API :

{
  "token": "jfadslkjfadsljf5645456446",
  "user": {
    "id": 12,
    "username": "test",
    "email": "[email protected]",
    "date_joined": "2023-08-02T20:29:00.274657Z",
    "userprofile": {
      "fullname": "test",
      "biography": "this is test",
      "profile_picture": "/images/Users/user_12/IMG_20230708_171948.jpg",
      // this is true
      "location": {"latitude": 1234.0, "longitude": 1234.0}
      // this is true
    }
  }
}

Actual result in the API:

{
  "token": "jfadslkjfadsljf5645456446",
  "user": {
    "id": 12,
    "username": "test",
    "email": "[email protected]",
    "date_joined": "2023-08-02T20:29:00.274657Z",
    "userprofile": {
      "fullname": "test",
      "biography": "this is test",
      "profile_picture": "/images/Users/user_12/IMG_20230708_171948.jpg",
      // this is my problem
      "location": "{"latitude":1234.0,"longitude":1234.0}"
      // this is my problem
    }
  }
}

Unfortunately "location" saved as String, Its must be saved as Map<String,double>