Mo. Rev. Stat. § 431.170: Action against assignor by assignee, when.

The assignee of a bond, nonnegotiable note or account, may maintain an action against the assignor, upon failure to obtain payment from the obligor, maker or debtor, only in one of the following cases:

(1) If he use due diligence in the institution and prosecution of a suit against the obligor, maker or debtor, for the recovery of the money or property due, or damages in lieu thereof;

(2) If the obligor, maker or debtor is insolvent, or is not a resident of this state, so that a suit would be unavailing or could not be instituted.