asp.net core app not serving ApiController route path - asp.net-mvc

Question

My asp.net core web application is not serving the ApiController route I have setup, however it used to work but I didn't change anything so idk why its not working now.
When I navigate to https://localhost:5001/api/Demo; it returns me to my sites homepage instead of running the action and displaying the data. the url in the address bar does change to …:5001/api/Demo, but does not display the data.
// controller
[ApiController]
[Route("api/[controller]")]
public class DemoController : ControllerBase
{
[HttpGet]
public string Index(string result)
{
return "test string";
}
}
public void ConfigureServices(IServiceCollection services)
{
services.AddControllersWithViews();
// In production, the React files will be served from this directory
services.AddSpaStaticFiles(configuration =>
{
configuration.RootPath = "ClientApp/build";
});
}
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
else
{
app.UseExceptionHandler("/Error");
// The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
app.UseHsts();
}
app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseSpaStaticFiles();
app.UseRouting();
app.UseEndpoints(endpoints =>
{
endpoints.MapControllerRoute(
name: "default",
pattern: "api/{controller=Demo}/{action=Index}/{result?}");
});
app.UseSpa(spa =>
{
spa.Options.SourcePath = "ClientApp";
if (env.IsDevelopment())
{
spa.UseReactDevelopmentServer(npmScript: "start");
}
});
}
==============================================
UPDATE: add configure method from startup class