In an Istisna'a contract, price and other necessary specifications must also be fixed and fully settled between the buyer and manufacturer/builder. The payments by the buyer in Istisna'a may be made in advance, during the period of construction reflecting stages of completion, or deferred to a specified future date. The contract of Istisna'a is a binding contract that cannot be cancelled unilaterally by either party once the manufacturing work starts. If the subject matter does not conform to the specification agreed upon, the buyer has the option to accept or to refuse the subject matter.