Mo. Rev. Stat. § 521.600

In order to disprove or avoid the debt and damages, or damages as mentioned in section 521.590, the defendant may petition the court rendering the judgment, or the court to which the records and papers may have been removed, setting forth the grounds on which he resists the demand of the plaintiff, and furnish the plaintiff with a copy of the petition fifteen days before the same shall be presented, with a written notice, endorsed on the copy, of the day and place when and where the petition will be presented.