Problem

During a file migration from Google Drive, the migration or preprocessing fails with the following error message:
Error:”unauthorized_client”, Description:”Unauthorized client or scope in request.”, Uri:”

Cause

The Google service account used for the migration does not have permission to access the user’s Google Drive.

Resolution

Follow this post to set the permissions correctly:
http://kb.cloudiway.com/how-to-create-an-admin-account-for-google-migration/
Make sure you add all the necessary scopes to set the permissions.