Qantas will refund or downgrade hundreds of passengers who were sold first-class flights at a huge discount last week because of a coding error.

“Unfortunately, this is a case where the fare was actually too good to be true,” a spokesperson for the Australian airline said.

On Thursday, when the erroneous offer was put up on its site, around 300 people quickly booked return flights between Australia and the US, paying 85% less than the usual first class fare.

Qantas said it will switch passengers who bought the bargain tickets into business class – one step down from first class – “at no additional cost”.

Customers paid a fraction of the usual price, with the discounted fares available on the site for about eight hours.

That meant they would have paid a few thousand Australian dollars for tickets that are meant to cost more than AUD20,000 (£10,000), entitling them to whiskey and champagne, an à la carte food menu, plus a memory foam mattress and a “pillow menu” when they want to sleep.

However, the airline’s terms and conditions state when customers book that if there is an error or mistake that is reasonably obvious in the fare price, the airline is entitled to cancel the booking and offer a full refund.

“As a gesture of goodwill, we’re rebooking customers in business class at no additional cost. Customers also have the option of a full refund,” Qantas said in a statement.

A passenger travelling business class would still be paying 65% less than usual for their ticket, the airline said.

It’s not the first time an airline has mistakenly offered discount prices – in 2019, Cathay Pacific accidentally sold $16,000 business-class seats for $675. In the end, it did honour the tickets for those lucky passengers.

But airlines don’t always honour tickets sold mistakenly for cheap: in 2018, British Airways cancelled tickets to Dubai and Tel Aviv which were sold for £1 instead of £200.