The wording for this question tells the story in someways.

Yes it is possible for the price of the ticket to go up between the time you paid and it is ticketed, even though you have made a booking.

The price on the booking is guaranteed at ticketing, not at booking. Sort of like this: you buy a ticket at 11:55 PM, and the price for the ticket expires at midnight. You started the booking process, you made payment, but it doesn’t actually get ticketed Until 12:05 AM. The discount fare is no longer available it expired at midnight.

Booking and ticketing are two different things. Regardless of whether payment has been made, the fare is based on time of ticketing not time of booking.

At https://Future.Travel we do our best to ensure ticketing takes place within 2 to 3 minutes of your booking payment. If for some reason we are not able to deliver the ticket at the price that you agreed on at check out, we return the funds.