Dependent on the device you are using depends where you enter the code. Please see our guide with images below.
Mobile site
Promotion codes can be added during checkout by entering your code into the promo code box.
App
Promotion codes can be added once your item has been added to your bag, on the ‘My Shopping Bag’ page just above the ‘Proceed to Checkout’ bar
Desktop/Laptop
Promotion codes can be added during checkout by entering your code into the promo code box.
Alternatively you can enter your code in the box shown below on most of the checkout screens.