Calendar Sync

I cannot get Wunderlist and Agenda to syncronize properly on all my devices (iPhone7Plus, Macbook Pro and iPad Pro). I changed a due date in Wunderlist with the hope that it would syncronize with Agenda on all my devices. It, instead, only syncronized on my iPhone 7Plus. How do I get all the devices in sync?

The question is whether Wunderlist syncs directly or indirectly with the calendar, but if you see the event update in the system calendar app, it should also do so in Agenda. Can you confirm that it indeed updates in the Calendar.app?

The Wunderlist to dos do not update in the system calendar. Do I understand correctly that they must appear in the system calendar app for them to appear in the Agenda app? And do I also understand that a change made on one device should sync across all the other devices that contain the Agenda app?

Thanks. Bryan