Do I need to link a calendar to for bookings?

Yes, you do need to connect your booking page to an external calendar for bookings.

Related: Which online calendars can I link to is not a standalone calendar. We use the existing events on your Google or Microsoft calendar to build a "grid" of available booking times. When you receive a new booking, an event is added to your linked calendar, and communicates with that event to trigger emails to you, your team member and your client.

Without connecting a linked calendar to your booking page, your booking page is unable to take bookings. 

You can create a new calendar in your Google or Microsoft account if your existing calendar is too full of other commitments.