Flight credits (https://www.quora.com/unanswered/How-can-I-use-an-airline-credit-toward-a-new-booking-through-Expedia) are generally subject to the airline's terms and conditions. Before using a credit, check its expiration date, eligible flights, passenger requirements, and redemption instructions. If the credit is eligible for use through Expedia, follow the applicable instructions during booking to apply it successfully.