When Booking Appointments using Appointment Search, by default (to improve performance) EXACT searches for 90 days into the future.

To search more than 90 days in advance SOE Support will be able to connect and change the below setting. You can request this setting be changed by Livechat, Email or Phone.
Configure, Settings (SOE permissions required) change: internal.appt search.max days without result to a greater number but be aware it may slow EXACT down slightly the higher this number goes.