Prepayment Orders are Sales Order which is paid before getting the goods or service. Business operates to provide service to a company or an individual. It depends on the business. On certain business the goods and service will be delievered when they get payment for the goods or ther service, its because of the nature of the goods, (service) or the business type. or the customer is unkown and new to operate the business first time.
In other scenario, Most of the services are paid partially before the delivery. In software projects, including the companies projects or freelancers project. The first case will start with upfront(advance) payment. Which will be the confirmation of the work to start. There are some problems as well. Some companies may not fullfill the customer needs, or doesnt meet the actual requirement. That's different scenario.
Services with prepaid
Most of the services are prepaid services, like Renting room in a hotel, movie tickets, online subscriptions( which has trial but its prepaid service when the trail expired), Travel fare, and much more. So the most of the services are paid before we get the service. Even Software As Service like TamilAccounting SaaS ERP
Prepaid Goods
When doing first business with a new customer or company, most of the business will start with prepaid orders. and in some customers they have huge overdues and unhealthy payment history, Those are all will be converted to give business when its prepaid for the orders.