A payment installment plan is an agreement between you and the Illinois Department of Revenue to pay your tax delinquencies using a monthly payment plan. A payment plan agreement outlines an installment plan to repay an outstanding balance over a specified time frame.An installment contract may be terminated in a variety of ways. Upon a buyer's default, a seller has available both statutory and common law remedies. The form is filledout as follows: A. CONSULTANT: Name of Consulting firm. By approving your request, we agree to let you pay the tax you owe in monthly installments instead of immediately paying the amount in full. An installment sale agreement is what a seller will put into place if they permit a buyer to pay for a property in increments or installments. Below is a list of forms and information that may be required to complete a Request for Proposal Response. Send agreement letter for installment payment via email, link, or fax. You can also download it, export it or print it out.