Okla. Admin. Code § 715:10-5-25
Members desiring to obtain credit for out-of-state service credit should submit to TRS a Verification of Out-of-State Service form . Included with the verification should be a list of all employment in the public schools of other states. Verification forms must be completed by the state retirement system for the employing state. TRS may require the member to provide such other evidence as may be required to establish the member's eligibility for out-of-state service. When the system determines the service 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 § 715:10-5-25