Mo. Rev. Stat. § 408.310
Any person may purchase or acquire or agree to purchase or acquire from any seller any retail time contract or account under a retail charge agreement on such terms and conditions and at such price as may be agreed upon between them. Filing of the assignment, notice to the buyer of the assignment, and any requirement that the purchaser or other assignee maintain dominion over the payments or the goods if repossessed shall not be necessary to the validity of a written assignment of such a contract or account as against creditors, subsequent purchasers, pledges, mortgagees and lien claimants of the seller. Unless the buyer has notice of the assignment of his contract or account, payment thereunder made by the buyer to the seller or to the last known purchaser or other assignee of such contract or account shall be binding upon all subsequent purchasers or other assignees.
§ 408.310, RSMo