YT Comment > Google Calendar Integration: Notify user when the selected appointment time slot is not available

A user from Youtube Comment is looking for a feature that notify users when the appointment time slot they selected is no longer available in Google Calendar. We have this option in Google Calendar, "Create event only if time slot is available" and it is working fine. But, it doesn't notify the form filler that the time slot they selected is not available. The user prefers to have a prompt informing them and allowing them to choose a different time slot.