Okla. Admin. Code § 715:10-5-15
Members desiring to obtain credit for military service credit should request in writing to be billed for the cost of the credit. Included with the request should be a certified copy or copies of the member's service record showing the dates and nature of the member's active military duty [Form DD-214, Form DD-217 or VA Certification of Active Duty]. TRS may require the member to provide such other evidence as may be required to establish the member's eligibility for military service. When the system determines the duty eligible for credit, it shall bill the member for the years of eligible credit. If the member becomes eligible for additional credit after the billing by TRS it shall be the responsibility of the member to request a second billing. Payment must be made by the date shown on the billing statement to avoid additional charges that may be required after the expiration of the billing date.
Okla. Admin. Code § 715:10-5-15