Please log into your account before applying any promo code and key in your promo code at the shopping cart page.
At the cart page, click 'Add". You will be able to key in your promo code in the pop-up.
You may wish to check that your promo code is reflected before checking out.
Promo codes will only apply when minimum spend amount or criteria is met for eligible customers. For full T&C, please click here and do a keyword search on the specific campaign. An illustration is attached below.

For further assistance, please submit your query via the web form and select "Promotions - Promo code eligibility" as the topic.