I have a peculiar problem where I am attempting to view submissions for multiple assignments using the Submissions API below:

/api/v1/courses/:course_id/students/submissions 

https://canvas.instructure.com/doc/api/submissions.html

I am an account admin, and I'm able to query for submissions using most every other API on the submissions page.  However, when I try to get multiple submissions for multiple assignments, I keep getting: 

{"status":"unauthorized","errors":[{"message":"user not authorized to perform that action"}]}

 At the moment, I'm just using a developer key. I've tried using multiple clients (browser, curl, etc.) with no luck.  My key is not 'scoped'.  I've created new keys.  I made sure that I'm in no other 'account roles', in case that was an issue.

I'm not sure what else to look at.  Any ideas out there?