Answer
It depends on the retailer. Some codes work on both the website and app, while others are app-only, website-only or limited to a particular checkout channel.
Look for channel restrictions in the promotion terms. If the same basket is available on both channels, compare the final price and any app-specific benefits before ordering.
What to check before checkout
Read the retailer’s current promotion terms, confirm that the code applies to the items in your basket, and make sure the expected saving appears before you pay.