To apply a coupon code:
After you select the Subscription or Single Purchase option on the Neurohacker Shop page (https://shop.neurohacker.com), move to the checkout page and click on the 'Have a discount code? Enter it here' link, where you can enter and apply the coupon to your order.
See attached pic for reference.
Please note: Some coupons are good for Subscriptions only, while others Single Purchase only. Be sure to reference your coupon code and place the order and corresponding discount accordingly.