La. Consolidated Public Retirement § 11:1307.2
Any member of the system with a minimum of twelve years of creditable service for regular retirement may, at the time of his retirement, purchase up to five years of service credit in one-year increments. The cost of service credit shall be determined in accordance with R.S. 11:158(C), and the member shall make a lump sum payment of the total cost prior to the date of retirement. He shall submit a letter of intent to purchase service credit with his application to retire not less than thirty days prior to the specified date of retirement. Additional service credit shall not be applied to the member's record until full payment is received. If the member does not retire within the thirty days after the payment is received, the full purchase cost shall be refunded to him and no additional credit will be applied to the service record.
La. Consolidated Public Retirement § 11:1307.2