This Master Sales Agreement (the "Agreement") is entered into between the buyer listed on the applicable Purchase Order ("Buyer") and Calimetrix, LLC. The monthly payment plan offers four monthly installments if you enroll before the semester due date.Payments will draft on or around the 10th of each month. A master service agreement (MSA) is a fundamental contract outlining the scope of the relationship between two parties. A master purchase agreement is a legally binding contract between buyer and seller, and typically relates to buying and selling goods rather than services. Except as otherwise provided in the SOW, ChannelAdvisor shall process automated payments as follows: the. Payment plan agreements are legally binding contracts that all parties involved should take seriously.