Create a Legally Binding Texas Car Loan Agreement in Minutes. 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. Watch this before you finance your next car (former dealer explains how to read a purchase contract) The retail installment contracts in the list below have been accepted as plain language contracts under the provisions of the Texas Finance Code. Sufficient income, credit and a history of paying debts on time are among the top criteria lenders seek in an applicant. My bank wants purchase agreement or bill of sale before sending out a check to the dealer. One contract is the car purchase or sales agreement where you contract with the dealer to purchase the vehicle. Then, you transfer the vehicle to them at the same time. The retail installment contracts in the list below have been accepted as plain language contracts under the provisions of the Texas Finance Code.