Flutter when serializing list of objects with jsonEncode the final string is getting cutt off

I have difficulty to convert a long list to JSON string. This is my main model which I want to convert to JSON string

class ActivityBookingRequest {
  int adminId;
  List<ActivityBookingDetail> activityBookingList;

  Map toJson() {
    List<Map> activityBookingListMap = this.activityBookingList != null
        ? this.activityBookingList.map((i) => i.toJson()).toList()
        : null;
    return {
      'adminId': adminId,
      'activityBookList': activityBookingListMap,
    };
  }
}

This is my sub-model which is the list I am trying to serialize!

class ActivityBookingDetail {
  int bookingId;
  int resourceId;
  int sourceId;
  String sourceName;
  int productId;
  String pickupDate;
  String cutOffDate;
  int adultNumber;
  int childrenNumber;

  ActivityBookingDetail(
    this.bookingId,
    this.resourceId,
    this.sourceId,
    this.sourceName,
    this.productId,
    this.pickupDate,
    this.cutOffDate,
    this.adultNumber,
    this.childrenNumber,
  );

  Map<String, dynamic> toJson() {
    return {
      'ssId': bookingId,
      'ssResourceId': resourceId,
      'sourceId': sourceId,
      'sourceName': sourceName,
      'productId': productId,
      'pickupDate': pickupDate,
      'cutOffDate': cutOffDate,
      'noAdult': adultNumber,
      'noChild': childrenNumber,
    };
  }
}

When I convert this to a JSON string if the list is long, the final JSON string is getting cut off!

{"adminId":213,{"ssId":4,"ssResourceId":4,"sourceId":1,"sourceName":"TRES","productId":3,"pickupDate":"2022-09-08T18:30:00","cutOffDate":"2022-09-08T18:30:00","noAdult":1,"noChi