This question has been asked several times and as per answers such as this it seems the API didn\'t support this then until recently as here which mentions that there are ne
A lot of stuff going on here :) However it seems the crux here is that you're expecting /Me/Calendars to include shared calendars. It does not. In order to access someone else's calendar that has been shared, you must access via the /Users/ URL.
So for example if bob@contoso.com logs in, and bill@contoso.com has shared his calendar with him, then:
/Me/Calendars would ONLY show calendars in Bob's mailbox/Users/bill@contoso.com/Calendars would show calendars Bill has shared with BobUpdate: It seems there's a blocking issue on our side. We're working on it.