A vehicle payment plan agreement is a contract between a buyer and seller of a vehicle that agrees to installment payments. Please include your driver's license number, full name, and date of birth on the Installment.This article explains how to get a loan to buy a car. To learn about other issues when buying a car, see our article on buying and keeping a used car. A car sale payment agreement is used when the purchase price of the car is paid in instalments. You are required to submit either payment of tax or proof that no tax is due before your vehicle can be titled. Both the buyer and the seller of the vehicle are required to fill out a Car Purchase Agreement Template. A payment plan agreement outlines an installment plan to repay an outstanding balance over a specified time frame.