The Facepay application (dapp) uses smart contracts on the Ethereum blockchain. All guest, merchant and transaction information that comprises the platform are written using these contracts. This is what has been missing that gave rise to all the vendor chaos at your cash register. It wasn't possible before the blockchain and the time is now.
Merchants use Facepay to manage accounts for your guests. Your guests don't need to download or do anything.
All the accounts are safely stored in the distributed ledger.
Guest checkout is the part you have the least control and the worst part of any guest visit. Facepay eliminates it.