One code covers the whole round

A counter order is one code, not one per drink. Four beers in an order is one scan at the bar, and the scan redeems all four at once. The guest shows it, the bar scans it, the round is handed over.

Merch and credits work the same way, each with their own code and their own scanner mode, so a merch order is scanned at the merch table and leaves the drinks alone.

A redeemed code shows as used on the guest's phone, so there is nothing to argue about a second time.