To pay with an e-gift card, you need the coupon code to hand.
The recipient will receive the coupon code to redeem the e-gift card via e-mail, using it as a payment method on one or more occasions.
If the coupon is used on a cart whose total is lower than the value of the e-gift card, the remaining balance will stay on the card and can be used for future purchases using the same coupon.
If the coupon is used on a cart of an amount higher than that of the e-gift card, it will be possible to complete the purchase by paying the difference at checkout.