The group life insurance policy must contain a provision that the policyholder is entitled to a grace period of 31 days for the payment of a premium due except the first, during which grace period the death benefit coverage shall continue in force, unless the policyholder gave the insurer written notice of discontinuance in advance of the date of discontinuance and in accordance with the terms of the policy. The policy may provide that the policyholder shall be liable to the insurer for payment of a pro rata premium for the time the policy was in force during the grace period.