It is possible that the tickets you bought are free tickets awarded by airlines to Ctrip, which sells a large number of tickets. Airlines sometimes give agents some free tickets, and agents will sell them to passengers when they don't use them, so the ticket money you pay is their profits. But in fact, the cost is zero, but personally, Ctrip will at least ask you whether the tickets you bought need to be reimbursed, and they can do so if they don't need to be reimbursed.