Lock Up Agreement
In legal terms, a contract is any agreement between parties to exchange things of value, such as goods and services for cash. A simple handshake agreement is legally binding, but its terms are not always provable if a dispute arises. However, you don't necessarily need pages upon pages of legalese. A basic contract agreement often works best for a simple business transaction.
Write or type up the date on the agreement to establish an effective date. List the parties involved in the agreement, using full business or individual names and titles. For example, you may title your business as the "Service Provider" and the customer as "Customer."