How can I convert a nested JSON to a Flutter model class?

The json you given is not valid json you can check it on json-validator online
i changed the json and make it valid here is the valid version

{
"movie": {
    "title": "String",
    "description": "String",
    "id": "String",
    "image": "String",
    "videos": [
        {
            "video": {
                "trailers": [
                    {
                        "trailers": {
                            "title": "String",
                            "option1": "String",
                            "option2": "String",
                            "option3": "String",
                            "availables": {
                                "first": true,
                                "second": true,
                                "third": true
                            }
                        }
                    }
                ]
            }
        }
    ]
 }
}

and the model for this is given as which i created using json to dart website

    class Movie {
  String? title;
  String? description;
  String? id;
  String? image;
  List<Videos>? videos;

  Movie({this.title, this.description, this.id, this.image, this.videos});

  Movie.fromJson(Map<String, dynamic> json) {
    title = json['title'];
    description = json['description'];
    id = json['id'];
    image = json['image'];
    if (json['videos'] != null) {
      videos = <Videos>[];
      json['videos'].forEach((v) {
        videos!.add(Videos.fromJson(v));
      });
    }
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = <String, dynamic>{};
    data['title'] = title;
    data['description'] = description;
    data['id'] = id;
    data['image'] = image;
    if (videos != null) {
      data['videos'] = videos!.map((v) => v.toJson()).toList();
    }
    return data;
  }
}

class Videos {
  Video? video;

  Videos({this.video});

  Videos.fromJson(Map<String, dynamic> json) {
    video = json['video'] != null ? Video.fromJson(json['video']) : null;
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = {};
    if (video != null) {
      data['video'] = video!.toJson();
    }
    return data;
  }
}

class Video {
  List<Trailers>? trailers;

  Video({this.trailers});

  Video.fromJson(Map<String, dynamic> json) {
    if (json['trailers'] != null) {
      trailers = <Trailers>[];
      json['trailers'].forEach((v) {
        trailers!.add(Trailers.fromJson(v));
      });
    }
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = {};
    if (trailers != null) {
      data['trailers'] = trailers!.map((v) => v.toJson()).toList();
    }
    return data;
  }
}

class Trailers {
  String? title;
  String? option1;
  String? option2;
  String? option3;
  Availables? availables;

  Trailers(
      {this.title, this.option1, this.option2, this.option3, this.availables});

  Trailers.fromJson(Map<String, dynamic> json) {
    title = json['title'];
    option1 = json['option1'];
    option2 = json['option2'];
    option3 = json['option3'];
    availables = json['availables'] != null
        ? Availables.fromJson(json['availables'])
        : null;
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = {};
    data['title'] = title;
    data['option1'] = option1;
    data['option2'] = option2;
    data['option3'] = option3;
    if (availables != null) {
      data['availables'] = availables!.toJson();
    }
    return data;
  }
}

class Availables {
  bool? first;
  bool? second;
  bool? third;

  Availables({this.first, this.second, this.third});

  Availables.fromJson(Map<String, dynamic> json) {
    first = json['first'];
    second = json['second'];
    third = json['third'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = {};
    data['first'] = first;
    data['second'] = second;
    data['third'] = third;
    return data;
  }
}