Only one way sync possible Appointments+

I installed the A+ plugin to my Wordpress website.
When I'm testing the plugin it only sync's in one way (Webstite -> Gcal). If I book an appointment in Gcal, the timeblok stays available on the website.

I've the settings for the (only) service provider on full sync (A+ <> Gcal) in the "Google Calendar settings tab"... What can be the problem? Thanks in advance!