Okla. Stat. tit. 47 § 427
The original summons or notice of suit filed with the Secretary of the Commission, as provided in Section 6 hereof, in all actions arising under the provisions of this act, shall be in form and substance the same as now provided in suits against residents of this State, except that that part of said summons pertaining to the return day shall be in substantially the following form, to-wit:
"and unless you appear thereto and defend in the District Court of Oklahoma in and for ________ county at the Court House in ________, Oklahoma, before noon of the sixtieth day following the filing of this summons with the Secretary of the Oklahoma Tax Commission of this State, default will be entered and judgment rendered against you by the Court in the amount of $____, if said Court is then in session in said county, and if the Court is not then in session, said default will be entered and judgment rendered by the Court on the first day of the succeeding term, or as soon thereafter as the same may be reached."
Plaintiff in any such action shall cause the original summons to be served as follows:
The notification provided for in this section shall be in substantially the following form, towit:
"To ________ (here insert the name of the defendant and his residence or last known place of abode as definitely as known): You will take notice that an original summons in a suit against you, a copy of which is hereto attached, was duly served upon you at Oklahoma City, Oklahoma, by filing copy of said summons on the ________day of ________, 19__, with the Secretary of the Oklahoma Tax Commission of the State of Oklahoma. Dated at ________, Oklahoma, this ________ day of ________, 19__.
_________________
Plaintiff
By _________________
Attorney for Plaintiff"
The term "restricted registered mail", as used herein, means mail which carries on the face thereof, in a conspicuous place where it will not be obliterated, the endorsement "Deliver to addressee only", and which also requires a return receipt.
Proof of the filing of a copy of said summons with the Secretary of the Oklahoma Tax Commission and proof of the mailing of said notification to said itinerant merchant shall be made by affidavit by the party doing said acts. All affidavits of service shall be endorsed upon or attached to the originals of the papers to which they relate. All proofs of service, including the return registry receipt, shall be forthwith filed with the clerk of the district court in which said cause of action is pending.
The foregoing provisions relating to service of the original summons on itinerant merchants shall not be deemed to prevent actual personal service in this state upon such itinerant merchants in the time, manner, form and under the conditions otherwise provided by law.
Okla. Stat. tit. 47, § 427