FAQ:
eGift Cards are all in U.S. dollars and can be purchased all over the world, providing gifts.marriott.com can validate the buyer’s banking information
The following Marriott Hotel Brands DO NOT accept Marriott GiftCards: Bulgari, Design Hotels, Homes & Villas by Marriott International, The Ritz-Carlton Destination Club.
I wonder if these can be used to pay for existing bookings?