Digital and Physical Gift Cards can be used online. However, Digital Gift Cards do take 24 hours to activate upon receipt.
If your Gift Card is not working, double-check the card number and PIN are correct, ensure you're entering your gift card into the correct box. You can find out how to add a Gift Card by clicking here.
You don't need to be signed in to your CC Account use your card and you don't need to spend it all in one transaction!