The nature of an agreement made under the provisions of Section 20 of the   Indian Contract Act would be: 

S. 20. Agreement void where both parties are under mistake as to matter of fact.— Where both the parties to an agreement are under a mistake as to a matter of fact essential to the agreement the agreement is void. Explanation.—An erroneous opinion as to the value of the thing which forms the subject-matter of the agreement, is not to be deemed a mistake as to a matter of fact.   ·         Void- null not having any force or validity. ·         Voidable- can become valid at the option of parties. ·         Valid- having force of law.