Whether you are leasing or financing, GAP can help protect you from coming out of pocket to pay expenses you may face with a total vehicle loss. Vehicle Payment Plan Agreement.A vehicle payment plan agreement is a contract between a buyer and seller of a vehicle that agrees to installment payments. If you're buying the car, you will be expected to sign a document called the Retail Installment Sales Contract (RISC). I'm going to show you stepbystep how to walk through and fill out the California residential purchase agreement or the RPA. CocoDoc collected lots of free vehicle purchase agreement with monthly payments for our users. California law prohibits a dealership from giving a customer a purchase agreement before the vehicle is on their property. Traditional vehicle financing allows you to own a new or used vehicle once all payments are completed. This legal document includes details about the vehicle, including its make, model, year, VIN, payment terms, and purchase price. If I were to sell a car on payments, I would draw up a contract that specified the details of the car (make, model, year, mileage).