There are two possible billing documents: invoices and proformas.
The two billing entities are the provider (the person that offers a certain service or product) and the customer (the person who benefits from the service or product).
The billing units that silver offers are the billing plan and the subscription, which allows to connect a customer to a plan.
Silver contains complex payment handling that includes payments, payment methods, payment processors and transactions.
We have put together some useful guides to help you better understand how Silver works and how you can easily add your own functionalities.