￥38 Off Towards Any New Purchase (常用) –下次购物时,总价减去38RMB.
Or
This coupon can redeem ￥38 RMB towards your next purchase.
此代金券不可兑换现金,每人次限用一张
This coupon has no cash value.Limit one coupon per person per visit.
最好再加一句：
Some restrictions may apply.（加在最后,意思可以加上其他限制）.
May not be combined with any other coupon (或许不能与其它优惠券一起使用,你有最终解释权）