An eligible employer joining the Oklahoma Firefighters Pension and Retirement System on or after July 1, 2000, may purchase up to five (5) years of credited service for each volunteer member of a volunteer fire department at the annual contribution rate in effect as of the date of the purchase, provided verifiable evidence of active firefighter service for the purchased years for each individual is provided to the System. Even though the participating municipality is exempt from contributions, contributions must be paid for a volunteer firefighter to receive purchased credited service. Payment for purchased credited service must be received by the System within six (6) months of the date the eligible employer becomes a participating municipality, and may be paid by the individual member. Six (6) months from the date the eligible employer becomes a participating municipality, any eligible prior credited service not purchased shall expire and not be available for determining benefits. Eligibility to receive purchased credited service shall be limited to those members of the new volunteer fire department enrolled at the time the eligible employer applies for affiliation with the System pursuant to Section 49-105.2 of Title 11 of the Oklahoma Statutes.