34 Tex. Admin. Code § 25.66
Members desiring to make deposits for military credit should request in writing to be billed for the cost of the credit. Requests should be addressed to Teacher Retirement System of Texas, 1000 Red River Street, Austin, Texas 78701-2698. Included with the request should be a certified or legible unaltered copy or copies of the member's military service record showing the dates and nature of the member's active duty. The system may require the member to make available to it such other evidence as may be required to establish the member's eligibility for service credit and the amount of deposits due. When the system determines the duty eligible for credit, it shall bill members for the total amounts of deposits and fees due for the credit at the last address of the member of which the system has record. The member must return the bill to the system with the total amount due for the military duty credit or with an installment payment agreement and all subsequent installment payments due. Deposits for military duty credit will not be accepted after date of death, except to the extent permitted under the laws and rules governing installment payments, or date of service retirement of a member.
34 Tex. Admin. Code § 25.66