Mo. Rev. Stat. § 522.090

No such suit shall be barred nor shall the amount which the plaintiff may be entitled to recover be affected, by any answer made by any surety in such bond, of a judgment recovered thereon, unless it be accompanied by an allegation that the sureties, or some of them, have been obliged to pay the damages on such judgment, or some part thereof, for want of sufficient property of the principal whereon to levy the same, or that they will be obliged to pay the same, or part thereof, for the same reason, nor unless such answer be verified by affidavit.