If you’ve set up your work schedule further in advance than what online booking currently shows to clients, the limiting factor is the How far in advance can appointments be booked setting, which is set to show clients a shorter period than the schedule you’ve actually prepared.

Example: let’s say today is January 1st and you’ve set up your work schedule all the way through March 31st. If your "Booking Window" is set to 1 month, the system will let clients book online no later than February 1st — regardless of the fact that your schedule reaches much further ahead. If you want clients to be able to book March slots as early as the start of January, you’ll need to change the "Booking Window" from 1 month to 3 months.

You can change the length of the booking window from the page Apps -> Staff -> Your profile -> Settings -> How far in advance can appointments be booked?

You’ll find more detailed instructions on this page.