How to make multiple checkbox selection with Getx

Question

All checkboxes were selected when I select only one checkbox. I tried most of solves in stackoverflow's post but those solves did not work for my code. Checkbox never be selected when I click one box Because value of isSelected inside Controller never change to true.

my model

class Sites {
  String? id;
  String? code;
  String? name;
  String? status;
  Timestamp? lastClickTime;
  int count;
  bool isSelected;
  

  Sites(
    this.id,
    this.code,
    this.name,
    this.status,
    this.lastClickTime,
    this.count,
    this.isSelected
  );
  
}

my controller

class SitesControllers extends GetxController {

  List<Sites> sitesList = <Sites>[].obs;
  bool isSelected = false;

  Future<void> getSites (String number) async {
    try {
      QuerySnapshot sites = await FirebaseFirestore.instance.collection("subscribers").doc(number).collection("sites").get();
      sitesList.clear();
      for(final site in sites.docs){
        sitesList.add(
          Sites(
            site.id,
            site['code'],
            site['name'],
            site['status'],
            site['lastClickTime'],
            0,
            isSelected
          )
        );
      }
      update();
    } catch (e) {
      Get.snackbar(
        "SitesControllers, ERROR", "> $e", 
        snackPosition: SnackPosition.BOTTOM);
    }
  }
}

my homepage.view

class HomePage extends StatelessWidget {
  String phoneNumber;
  HomePage({super.key, required this.phoneNumber});

  SitesControllers sitesControllers = Get.put(SitesControllers());
  CountController countController = Get.put(CountController());

  int actionController = 0;

  @override
  Widget build(BuildContext context) {
    return GetBuilder<SitesControllers>(
        init: SitesControllers(),
        initState: (_) {},
        builder: (sitesControllers) {
          sitesControllers.getSites(phoneNumber);
          return Scaffold(
            backgroundColor: Colors.white,
            appBar: buildAppBarField("Home Page", false),
            body: buildSiteField(context, phoneNumber),
            floatingActionButtonLocation:
                FloatingActionButtonLocation.centerDocked,
            floatingActionButton: buildFloatActionButtonField(),
            bottomNavigationBar: buildBottomNavigationBarField(),
          );
        });
  }

  Widget buildSiteField(BuildContext context, String number) {
    return Padding(
      padding: EdgeInsets.symmetric(vertical: context.dynamicHeight(0.02)),
      child: Obx(() => ListView.builder(
          itemCount: sitesControllers.sitesList.length,
          itemBuilder: (BuildContext context, index) {
            //countController.counter(number, sitesControllers.sitesList[index].id.toString());
            return Padding(
              padding: EdgeInsets.symmetric(
                  horizontal: context.dynamicWidth(0.04),
                  vertical: context.dynamicHeight(0.005)),
              child: Container(
                  decoration: BoxDecoration(
                      color: Colors.white,
                      borderRadius: BorderRadius.circular(15),
                      border: Border.all(
                          color: ColorConstants.mainColor, width: 2)),
                  child: ListTile(
                    visualDensity: VisualDensity.compact,
                    dense: true,
                    isThreeLine: true,
                    onTap: () { buildListTileOnTapField(index, number); },
                    leading: buildListTileLeadingField(
                        context,
                        sitesControllers.sitesList[index].name.toString(),
                        index),
                    subtitle: buildListTileSubstitleField(index),
                    trailing: buildListTileTrailingField(context, index),
                  )),
            );
          })),
    );
  }

  // WIDGETS
  Widget buildListTileLeadingField(BuildContext context, String siteName, int index) {
    return actionController == 1
        ? Checkbox(
            checkColor: Colors.white,
            value: sitesControllers.sitesList[index].isSelected,
            onChanged: (bool? value) {
              sitesControllers.sitesList[index].isSelected = !sitesControllers.sitesList[index].isSelected;
            },
          )
        : Padding(
            padding:
                EdgeInsets.symmetric(vertical: context.dynamicHeight(0.007)),
            child: Text(
              siteName.substring(0, 1).toUpperCase(),
              style: const TextStyle(
                  color: ColorConstants.siteFirstLetter,
                  fontSize: 25,
                  fontWeight: FontWeight.bold),
            ),
          );
  }

 ...

}