请大家帮助准确翻译一下jetstar的旅行勾销换券的声名。谢谢

龙吟九天

The voucher can be redeemed up to the value stated on the voucher in one booking only within 6 months of issue, for travel within 十二 months of the booking date. A fare difference, if any, will apply.
6个月内兑换?
券无效期十二个月吗？