Many, if not the majority of services that offer backorder services hold auctions when they have concurrent backorders, which puts buyers in a wallet-versus-wallet situation.
On Epik, backorders work on a first-come-first-served basis and the first buyer to have paid for the backorder gets the domain if Epik catches it.
If Epik doesn’t succeed in catching the domain the backorder will be canceled and you’ll be refunded the amount to In-Store Credit automatically.