Mutual Mistake Regarding Planning Authorization Voids Real Property Sale Contract

A contract for the sale of real property, entered into under the mistaken belief by both parties that a municipal planning authorization, necessary for the intended use of the property, had been granted, was deemed voidable because the lack of authorization constituted a failure of the essential quality of the thing sold, which was the basis of the purchasers' consent. The court affirmed the lower court's decision, reasoning that while the mistake did not relate to the property's fundamental substance, it concerned a quality directly essential to the commercial purpose of the purchase as understood by both contracting parties, rendering the contract illicitly formed due to a mutual, material error regarding a necessary legal prerequisite.