Cannot resolve scoped service 'Elsa.Workflows.Runtime.Services.BackgroundTaskDispatcher' from root provider

Hi,
I worked on some of the sample applications provided in ELSA guides. One of them is https://v3.elsaworkflows.io/docs/guides/external-app-integration.

This application ran very well as per documentation.
However, when I took the source code (elsa-core) and built the solution. I chose "Elsa.Server.Web" as a startup project. I made the necessary changes in

"Program.cs" and
// Configure ASP.NET authentication/authorization.
// Default Identity features for authentication/authorization.
// Use email activities.

"app_settings.json" e.g. "Webhooks" and "AllowedHosts" entries, as specified in the guide.

My development environment is on Windows 10.

I am getting the following error. What could be the reason? I would appreciate your help in this regard.

warn: Elsa.Workflows.Middleware.Activities.ExceptionHandlingMiddleware[0]
An exception was caught from a downstream middleware component
System.InvalidOperationException: Cannot resolve scoped service 'Elsa.Workflows.Runtime.Services.BackgroundTaskDispatcher' from root provider.
at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType)
at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider provider)
at Elsa.Workflows.Runtime.Features.WorkflowRuntimeFeature.<>c.<.ctor>b__0_9(IServiceProvider sp) in D:\ELSA3.0\els-core-github\src\modules\Elsa.Workflows.Runtime\Features\WorkflowRuntimeFeature.cs:line 89
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSiteMain(ServiceCallSite callSite, TArgument argument)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitRootCache(ServiceCallSite callSite, RuntimeResolverContext context)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.Resolve(ServiceCallSite callSite, ServiceProviderEngineScope scope)
at Microsoft.Extensions.DependencyInjection.ServiceProvider.CreateServiceAccessor(ServiceIdentifier serviceIdentifier)
at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType)
at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider provider)
at Elsa.Workflows.WorkflowExecutionContext.GetRequiredService[T]() in D:\ELSA3.0\els-core-github\src\modules\Elsa.Workflows.Core\Contexts\WorkflowExecutionContext.cs:line 400
at Elsa.Workflows.ActivityExecutionContext.GetRequiredService[T]() in D:\ELSA3.0\els-core-github\src\modules\Elsa.Workflows.Core\Contexts\ActivityExecutionContext.cs:line 489
at Elsa.Workflows.Runtime.Activities.RunTask.ExecuteAsync(ActivityExecutionContext context) in D:\ELSA3.0\els-core-github\src\modules\Elsa.Workflows.Runtime\Activities\RunTask.cs:line 98
at Elsa.Workflows.Activity.Elsa.Workflows.Contracts.IActivity.ExecuteAsync(ActivityExecutionContext context) in D:\ELSA3.0\els-core-github\src\modules\Elsa.Workflows.Core\Abstractions\Activity.cs:line 218
at Elsa.Workflows.Middleware.Activities.DefaultActivityInvokerMiddleware.ExecuteActivityAsync(ActivityExecutionContext context) in D:\ELSA3.0\els-core-github\src\modules\Elsa.Workflows.Core\Middleware\Activities\DefaultActivityInvokerMiddleware.cs:line 103
at Elsa.Workflows.Runtime.Middleware.Activities.BackgroundActivityInvokerMiddleware.ExecuteActivityAsync(ActivityExecutionContext context) in D:\ELSA3.0\els-core-github\src\modules\Elsa.Workflows.Runtime\Middleware\Activities\BackgroundActivityInvokerMiddleware.cs:line 42
at Elsa.Workflows.Middleware.Activities.DefaultActivityInvokerMiddleware.InvokeAsync(ActivityExecutionContext context) in D:\ELSA3.0\els-core-github\src\modules\Elsa.Workflows.Core\Middleware\Activities\DefaultActivityInvokerMiddleware.cs:line 64
at Elsa.Workflows.Middleware.Activities.NotificationPublishingMiddleware.InvokeAsync(ActivityExecutionContext context) in D:\ELSA3.0\els-core-github\src\modules\Elsa.Workflows.Core\Middleware\Activities\NotificationPublishingMiddleware.cs:line 29
at Elsa.Workflows.Middleware.Activities.ExecutionLogMiddleware.InvokeAsync(ActivityExecutionContext context) in D:\ELSA3.0\els-core-github\src\modules\Elsa.Workflows.Core\Middleware\Activities\ExecutionLogMiddleware.cs:line 41
at Elsa.Workflows.Middleware.Activities.ExceptionHandlingMiddleware.InvokeAsync(ActivityExecutionContext context) in D:\ELSA3.0\els-core-github\src\modules\Elsa.Workflows.Core\Middleware\Activities\ExceptionHandlingMiddleware.cs:line 47