iCal: Calendar synchronization with Google Calendar works no longer

Why can't OptiOffice sync with my Google Calendar? The following points explain why Google Calendar cannot be synchronized with OptiOffice Calendar.

1) Individual participants, the type of appointment, of an appointment cannot be edited in Google Calendar.
2) In the Google calendar, you can only delete an entire appointment or move the appointment.
3) You can add an appointment in the Google Calendar, but without assigning contacts or an appointment type.
4) Appointments created in Google can therefore not be billed using an appointment check.
5) Appointments created in Google cannot consider memberships or limits or packages.