With record number of travelers going to Europe I would wait a few days to hear from them. Unless it is a private tour they have to check the ship, the date and see if a group has already been started for that particular excursion. If there isn't one they usually reply that they will start a group and let you know when the minimum reservations have occurred. I have only used them for shared excursions and I don't know what the procedure is for booking a private tour.
It may also depend on when you are sailing. They may still be having staffing problems or lack of tour guides in all of their ports. There is a lot of follow up closer to your sailing once booked. Hope this helps.