I have this same problem, and I am looking for a solution; I also used the function proposed by Imke Feldman and it worked perfectly in Power BI Desktop, however, I can not authenticate the source to schedule automatic updating.
If another function is required to allow authentication, I don't understand where this function should be inserted.
I opened a support ticket 5 months ago, still no solution. Every month they send my issue to another engineer, but no one helped so far. and sincerely, and I think they never will, as dropbox is rival to onedrive... sad.