The parties shall notify the tribunal of any changes to the above-referenced information within ten days of the effective date of the change. In subsequent support actions between the obligor and the obligee or their assignees, upon sufficient showing that diligent effort has been made to ascertain the location of the party, delivery by first-class mail of written notice to the obligor and the obligee at the residential or employer address most recently filed with the tribunal constitutes service of process.
S.C. Code § 63-17-450