Mo. Rev. Stat. § 430.240
No such lien shall be effective, however, unless a written notice containing the name and address of the injured person, the date of the accident, the name and location of the hospital and the name of the person or persons, firm or firms, corporation or corporations alleged to be liable to the injured party for the injuries received shall be sent by certified mail with return receipt requested to the person or persons, firm or firms, corporation or corporations, if known, alleged to be liable to the injured party, if known, for the injuries sustained prior to the payment of any moneys to such injured person, his attorneys or legal representative, as compensation for such injuries. Such hospital shall send by certified mail with return receipt requested a copy of such notice to any insurance carrier, if known, which has insured such person, firm or corporation against such liability.
§ 430.240, RSMo