To apply a coupon code:
After you press the Buy Now button for the Subscription or Single Purchase option on the Neurohacker Shop page (https://neurohacker.com/shop), you will find the ability to add a discount code o the right side of the screen under Have a discount code?
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.