angular 8 fails going to lazy loaded modules directly after prod deploy

I have downloaded lazy-loading-ngmodules.zip from https://angular.io/guide/lazy-loading-ngmodules. I ran the app using ng serve with no problem. I can browse url http://localhost:4200 and click on Customers and Orders which both are lazy loading modules. I also can directly browse the url – http://localhost:4200/customers.

Then I built production version using ng build –prod and hosted it on IIS. I can browse the url http://localhost:80 and click on Customers and Orders to navigate to lazy loading modules. No problems!!! However, if I browse directly to the url http://localhost:80/customers, I got HTTP 404 Error. Why??? I need to directly browse to the lazy loading modules. How should I do it?

Thanks in advance!!!