amount
The part of the gift card's balance that covers the cart.
This is at most balance and at most what is left to pay after the gift cards applied
before it. Several gift cards on the same cart therefore split the total between them, and the amount
changes whenever the cart is repriced or another gift card is applied or removed.
Null when the gift card covers nothing, which is what a gift card that has become unusable looks like until the next time the cart is changed.
Arguments
amount doesn't take any arguments.
Type
This field resolves to Money, which has the following fields: