Let's walk through the typical issues that might be causing your Url.Action call to return null when generating the confirm email callback URL, along with fixes for each:

• Mismatched action/controller naming
  ASP.NET expects action method names to use PascalCase (like ConfirmEmail), not kebab-case (confirm-email). If your controller method is named ConfirmEmail, you need to pass that exact string to Url.Action—the framework won't automatically convert kebab-case to PascalCase here. Double-check that your action name in the code matches the actual method name in your AccountController.

• Incorrect controller class name
  Make sure your controller class is named AccountController (the Controller suffix is mandatory). If it's named something like Account or AccountsController, Url.Action won't be able to locate it, resulting in a null return value.

• Invalid or missing Request.Scheme
  If you're running this code outside of an HTTP request context (like a background service, console app, or a place where Request isn't available), Request.Scheme will be null or empty. Url.Action needs a valid scheme (http/https) to build a full absolute URL. You can fix this by hardcoding the scheme temporarily for testing, or ensuring you're in a valid request context:

  var callbackUrl = Url.Action("ConfirmEmail", "Account", new { token, email }, "https");
  

• Uninitialized UrlHelper
  If this code isn't running inside a controller, view, or a service where UrlHelper is properly injected, the Url object might not be set up correctly. For custom services, you'll need to inject IUrlHelperFactory and ActionContext to create a valid UrlHelper instance:

  // In your service constructor
  private readonly IUrlHelperFactory _urlHelperFactory;
  private readonly ActionContext _actionContext;
  
  public YourService(IUrlHelperFactory urlHelperFactory, ActionContext actionContext)
  {
      _urlHelperFactory = urlHelperFactory;
      _actionContext = actionContext;
  }
  
  // When generating the URL
  var urlHelper = _urlHelperFactory.GetUrlHelper(_actionContext);
  var callbackUrl = urlHelper.Action("ConfirmEmail", "Account", new { token, email }, "https");
  

• Broken routing configuration
  Check your route setup (in Startup.cs for .NET Core or RouteConfig.cs for .NET Framework) to ensure it includes placeholders for controller and action. The default route should look something like this:

  app.UseEndpoints(endpoints =>
  {
      endpoints.MapControllerRoute(
          name: "default",
          pattern: "{controller=Home}/{action=Index}/{id?}");
  });
  

  If your routes don't include {controller} and {action}, Url.Action can't map your controller/action pair to a valid URL path.

内容的提问来源于stack exchange，提问作者Muhammad farhan