Dunning Process not picking delinquent/past due account

I completed most of the required setup for Customer profile class, aging bucket, dunning setup. All my setup is out of the box except I defined different aging bucket.

When I run the dunning process its is not printing dunning for the past due account. Is there any setup document which shows all the required setup? We are not using advance collection. We are using standard receivables with basic aging bucket and standard dunning letter out of the box.

Any help will be greatly appreciated.

Many Thanks.