Gainz Box Coupon: Get 40% Off Your First Month! Last updated by Hello Subscription on November 10, 2019. Subscription Box Coupons & Deals / Gainz Box Coupons Hello Subscription may earn compensation via links in this post. Read the full disclosure Save for Later Notification Gain[z] Box has a new sale! Get 40% off your first month! Just use the code GZ40. Valid to new subscribers only. Get 40% off at Gain[z] Box! Are you getting Gain[z] Box?