Instant gift cards cannot be returned, canceled, or refunded after purchase. However, for each one you've brought, you'll see an expiry date which you can use whenever is best for you.
If you've arranged an upcoming Payday gift card that hasn't yet been purchased from your salary, these can be canceled anytime via the app by following the below:
Head to your Gift Cards (Hub>Discounts>My Gift Cards)
Find the gift card under the Upcoming section
Hit Cancel
Confirm