Okla. Stat. tit. 51, § 60

The Senate, when sitting as a court of impeachment, shall appoint a day for hearing the impeachment, and the accused shall be required by a summons by the clerk to appear on that day. The summons shall be served by delivering a copy of the same and of the articles of impeachment to the accused, in person if to be found, or by leaving the copies at his residence with some member of his family over sixteen (16) years of age.