About Retainers
A retainer is a fee paid in advance in order to secure your services. It may also be called a down payment, a prepayment, or an upfront fee. In Billings, retainers are grouped by clients; if you receive money from a client as a prepayment for services you will render, you can deposit it into the retainer, and later apply that retainer as payment against an invoice.
Billings keeps track of the amount of money in the retainer. When you add a payment using retainer as the method, or when you create an invoice that uses the retainer, Billings reduces the available retainer balance.