Declined invitations in Google calendar block availability in YouCanBook.me
If you are invited to an event via Google calendar and you decline it Google can still report that event to YouCanBook.me as blocking your availability.
Make sure your Google Calendar is displaying events you've declined. Under the Week menu, select Show declined events.
Make sure that is checked and then you'll be able to see the events that you have previously declined. Set declined events to "Free" or delete them from your calendar and free up your availability in YouCanBook.me.