(Google Calendar) Time to go back on WhatsApp in case it canceled.

It’s not an idea, it’s a question.
After linking Google Calendar to use it for booking appointments my problem is that if someone books an appointment and wants to cancel it, the time he booked doesn’t appear to other clients.

An Example:
Let’s say I select 9:00 a.m. and 5:00 pm for any of my clients to make an appointment.
Through WhatsApp, If someone chooses 5:00 p.m. and cancels before the time comes, the time should be available for others. But it isn’t.
I can manually delete the appointment from Google Calendar, but I need the time to go back in case another client wants to make an appointment at the same time.