You need to follow these steps to apply a discount code:
1. Add the product that you would like to buy to your basket.
2. Click on View basket.
3. Go to Select discount and all the gift vouchers assigned to your profile will appear.
Under these you will have the option to add the code.
4. Click, and type in your code.
5.Finally, accept it.
Congratulations! You have made your purchase using your discount code in the app!