Unauthorized error when accessing files through API

I am attempting to access project output files through the CGC API. I am using the sevenbridges python package. I have run the code provided on the documentation for accessing projects with initialization via environment variables (https://pypi.python.org/pypi/sevenbridges-python). However, an Unauthorized error is returned. I have double checked and the authentication token I am using is correct. What would be the reason for this?