The fare hold for a flight ticket is about to expire today. How can I remind the client without sounding pushy?

I had a client today whose international flight fare hold was expiring in the afternoon, and he was still waiting for confirmation from his family. In the past, just sending a 'payment is due' message tended to annoy clients. This time, I first checked the fare rules, ticketing deadline, change fees, and price fluctuations for the same route, then sent a very short message: stating when the…