I am using Flutter with the PagedMasonryGridView widget to implement infinite scroll pagination. However, the lazy loading functionality is not working as expected. Instead of loading data on user scroll, all data is fetched at once. I can see multiple API calls in the logger, but it appears to fetch all data in one go. I am using the Provider package for state management.

My Widget

class AgencyProfile extends StatelessWidget {
  const AgencyProfile({super.key});

  @override
  Widget build(BuildContext context) {
    double screenWidth = MediaQuery.of(context).size.width;
    double screenHeight = MediaQuery.of(context).size.height;

    return Scaffold(
      body: SizedBox(
        child: Consumer<AgencyProfileProvider>(
          builder: (context, provider, child) {
            if (provider.agencyProfileModel != null &&
                provider.agencyProfileModel!.success &&
                !provider.isAgencyLoading) {
              return NestedScrollView(
                headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
                  return <Widget>[
                    SliverList(
                      delegate: SliverChildListDelegate(
                        [
                          // Header content here
                        ],
                      ),
                    ),
                  ];
                },
                body: PagedMasonryGridView<int, Datum>(
                  shrinkWrap: true,
                  primary: true,
                  pagingController: provider.pagingController,
                  padding: const EdgeInsets.only(top: 0),
                  crossAxisSpacing: 1,
                  cacheExtent: 9999,
                  mainAxisSpacing: 1,
                  addAutomaticKeepAlives: true,
                  builderDelegate: PagedChildBuilderDelegate<Datum>(
                    itemBuilder: (context, item, index) {
                      return Container(
                        width: screenWidth / 3.1,
                        height: screenHeight / 3.6,
                        decoration: const BoxDecoration(
                          color: Colors.black45,
                        ),
                        // Item content here
                      );
                    },
                  ),
                  gridDelegateBuilder: (int childCount) {
                    return SliverSimpleGridDelegateWithMaxCrossAxisExtent(
                      maxCrossAxisExtent: screenWidth / 3,
                    );
                  },
                ),
              );
            } else if (provider.agencyProfileModel != null &&
                !provider.agencyProfileModel!.success) {
              return const Center(
                child: Text("Something went wrong! Please try again later."),
              );
            }
            return const Center(
              child: CircularProgressIndicator(),
            );
          },
        ),
      ),
    );
  }
}

My Provider

class AgencyProfileProvider extends ChangeNotifier {
  // other codes

  static const _pageSize = 10;
  final PagingController<int, Datum> pagingController =
      PagingController(firstPageKey: 0);
  final ScrollController _scrollController = ScrollController();

    
  Future<void> initData(int id) async {
    getAgencyDetails(id);
    WidgetsBinding.instance.addPostFrameCallback((_) {
      pagingController.addPageRequestListener((pageKey) {
        _fetchPage(id, pageKey);
      });
    });
  }


  Future<void> _fetchPage(int agencyId, int pageKey) async {
    try {
      await Future.delayed(const Duration(seconds: 1));
      final newItems = await AgencyDetailRepository().getAgencyTours(
          agencyId.toString(), _pageSize, (pageKey * _pageSize));
      final isLastPage = newItems.data!.length < _pageSize;
      if (isLastPage) {
        pagingController.appendLastPage(newItems.data!);
      } else {
        final nextPageKey = pageKey + 1;
        pagingController.appendPage(newItems.data!, nextPageKey);
      }
    } catch (error) {
      pagingController.error = error;
    }
  }

   // other codes

} 

main.dart

ChangeNotifierProvider(
            create: (context) => AgencyProfileProvider()..initData(2),
            child: const AgencyProfile(),
          )