1. Go on the Promotion page and Check the available promotions: Promotion Page
2. Click the code and popup will appear, Press Ctrl + C then Enter.
3. Browse the service in which coupon applies.
4. During order it will ask you, Apply the coupon if you have any.
5. Paste the coupon and Press Validate button.
6. Discount will be applied on your cart.
This means the coupon you select is not for the service you select.
Contact @ Support@obhost.org for any query.