RangeError (index): Invalid value: Not in inclusive range 0..5: 12 – Flutter

this is my first provider class. I’m trying to retrieve the name of my item from my list

before getting this error I got another error that said ‘_internallinkedhashmap<string, dynamic>’ I search that online and add .cast<String, dynamic>().
now I’m getting this one. is this something to do with my list length

import 'package:ecnomic/provider/provider.dart';
import 'package:flutter/material.dart';
import 'package:flutter/src/widgets/container.dart';
import 'package:flutter/src/widgets/framework.dart';
import 'package:provider/provider.dart';
import '../service/colors.dart';

class ItemProperties extends StatefulWidget {
  const ItemProperties({super.key});

  @override
  State<ItemProperties> createState() => _ItemPropertiesState();
}

class _ItemPropertiesState extends State<ItemProperties> {
  @override
  Widget build(BuildContext context) {
    List items = [];
    final itemprovider =
        Provider.of<onlineShopingProvider>(context, listen: false);
    items = itemprovider.getOnlineItem;

    return Container(
        color: Colors.blue,
        height: 500,
        width: double.infinity,
        child: GridView.builder(
            gridDelegate: const SliverGridDelegateWithFixedCrossAxisCount(
              crossAxisCount: 2,
              crossAxisSpacing: 5,
              // mainAxisSpacing: 10,
              // childAspectRatio: 3 / 2,
            ),
            itemCount: 20,
            itemBuilder: ((context, index) {
              return
                  // Card(
                  //     color: Colors.amber,
                  //     child:
                  Column(
                children: [
                  Image.network(
                      'https://hips.hearstapps.com/hmg-prod/images/2020-bmw-750i-xdrive-252-1566180109.jpg?crop=1.00xw:0.927xh;0,0.0366xh&resize=2048:*'),
                  Text('$index'),
                  Text(
                      '${itemprovider.getOnlineItem[index].item_name.cast<String, dynamic>()}'),
                ],
              );
              //);
            })));
  }
}

and this is my provider class

import 'package:flutter/material.dart';

class onlineShopingProvider with ChangeNotifier {
  final dynamic _onlineitem = [
    {
      "item_id": 2,
      "item_name": "Jeep Wrangler Sahara",
      "item_price": "80000",
      "item_image":
          "https://www.motortrend.com/uploads/sites/11/2020/01/2020-Jeep-Wrangler-Unlimited-Sahara-4x4-25958.jpg?fit=around%7C875:492",
      "category_id": 22,
      "category_name": "Jeep",
      "item_color": "#FF0000"
    },
    {
      "item_id": 2,
      "item_name": "Jeep Wrangler Sahara",
      "item_price": "80000",
      "item_image":
          "https://www.motortrend.com/uploads/sites/11/2020/01/2020-Jeep-Wrangler-Unlimited-Sahara-4x4-25958.jpg?fit=around%7C875:492",
      "category_id": 22,
      "category_name": "Jeep",
      "item_color": "#FF0000"
    },
    {
      "item_id": 18,
      "item_name": "Jeep Grand Cherokee Summit",
      "item_price": "80000",
      "item_image":
          "https://hips.hearstapps.com/hmg-prod/images/2023-jeep-grand-cherokee-summit-4x4-101-1667328305.jpeg?crop=0.617xw:0.520xh;0.353xw,0.451xh&resize=2048:*",
      "category_id": 22,
      "category_name": "Jeep",
      "item_color": "#FF0000"
    },
    {
      "item_id": 3,
      "item_name": "BMW X5",
      "item_price": "100000",
      "item_image":
          "https://www.motortrend.com/uploads/2022/11/2023-BMW-X5-xDrive40i-front-three-quarter-view-11.jpg?fit=around%7C875:492.1875",
      "category_id": 23,
      "category_name": "BMW",
      "item_color": "#000000"
    },
    {
      "item_id": 4,
      "item_name": "BMW 7 Series",
      "item_price": "100000",
      "item_image":
          "https://hips.hearstapps.com/hmg-prod/images/2020-bmw-750i-xdrive-252-1566180109.jpg?crop=1.00xw:0.927xh;0,0.0366xh&resize=2048:*",
      "category_id": 23,
      "category_name": "BMW",
      "item_color": "#000000"
    },
    {
      "item_id": 4,
      "item_name": "BMW 8 Series",
      "item_price": "107000",
      "item_image":
          "https://www.caranddriver.com/photos/g27011971/2020-bmw-7-series-drive-gallery/",
      "category_id": 23,
      "category_name": "BMW",
      "item_color": "#000000"
    }
  ];

  final dynamic shopingCatagory = [
    {
      "category_id": 22,
      "category_name": "Jeep",
      "category_image": "https://pngimg.com/uploads/jeep/jeep_PNG95.png"
    },
    {
      "category_id": 24,
      "category_name": "Toyota",
      "category_image":
          "https://www.freepnglogos.com/uploads/toyota-logo-png/toyota-logos-brands-logotypes-0.png"
    },
    {
      "category_id": 23,
      "category_name": "BMW",
      "category_image":
          "https://pngimg.com/uploads/bmw_logo/bmw_logo_PNG19714.png"
    }
  ];

  get getOnlineItem => _onlineitem;
  get getShopingCatagory => shopingCatagory;
}