If a customer is stopping off in a higher level destination as the plane needs to refuel or they are waiting for a connecting flight for less than 72 hours, then they can travel on the lower level destination.
As long as they had to stop for the plane for the above reasons and haven't just added the extra destination to their itinerary, then they are able to leave the airport, stay in a hotel etc. Please note if the customer is going on a cruise - the stopover rule doesn't apply, they need to book for the higher level destination as this is part of their itinerary.