Okla. Stat. tit. 51 § 96
Upon the filing of the complaint or petition for the writ of ouster, a summons shall issue for the defendant to appear and answer the same within twenty (20) days of the service thereof, and there shall accompany the summons and be served upon the defendant a copy of the complaint or petition filed against him.
The petition and answer shall constitute the only pleadings allowed, and all allegations in the answer shall be deemed controverted, and any and all questions as to the sufficiency of the petition or complaint shall be raised and determined upon the trial of the cause; and if said petition is held insufficient in form, the same shall be amended at once, and such amendment shall not delay the trial of the case.
Okla. Stat. tit. 51, § 96