The sync with Outlook is one way only, from Bookeo to Outlook. If you want to use a 2 way sync, you can sync Bookeo Calendar 2-way with Google Calendar, then sync Google Calendar 2-way with Outlook.
in your Bookeo account, click on "Calendar" and then on the iCal button at the bottom
copy the web address of your calendar
In Outlook, click on the 'Open Calendar' button in the menu ribbon
- Select "From Internet..." from the menu
paste the web address you copied earlier, and save the changes