Mo. Rev. Stat. § 288.125: Voluntary payments by employer.

Any employer may make voluntary payments in addition to the contributions required under this law, which shall be credited to his account, in accordance with regulations established by the division. Such payments shall be included in the employer's account as of the preceding calculation date if they are made on or before the following January fifteenth. Such voluntary payments when accepted from an employer will not be refunded in whole or in part.