Getting MailboxNotEnabledForRESTAPI - no clue why

Question

I have created a ms account yesterday. And I have created an azure app. I am the owner. I am always getting MailboxNotEnabledForRESTAPI. But why? Using the graph API /me/calendars. /me query works though Grant Permissions are correct. Graph Explorer shows the same error. I even paid for office 365 subscription, because I though this might be the cause. I have read the docs about MailboxNotEnabledForRESTAPI. The docs confuse me a lot. I'd appreciate an explanation of why this is happening to me.

Answer 1

I have solved it by re-creating the app as "multi tenant with personal ms accounts".