Google Drive to Dropbox Migration Guide
Enable OAuthentication 2.0 within your Google admin portal, to grant MigrationWiz access to Google Apps. KB005019
If you are migrating from multiple domains, repeat these steps for each domain.
Under Authorized API clients > Client Name > Enter: 794841909041-4ujv1ss1o7m7kqm3gtqd06bklietmmde.apps.googleusercontent.com
Under One or more API Scopes, enter the scope for Google Apps as Source (read-only scopes):
https://mail.google.com/, https://www.google.com/m8/feeds, https://www.googleapis.com/auth/contacts.readonly, https://www.googleapis.com/auth/calendar.readonly, https://www.googleapis.com/auth/admin.directory.group.readonly, https://www.googleapis.com/auth/admin.directory.user.readonly, https://www.googleapis.com/auth/drive
OAuth administrative credentials will not function properly with Google Apps for Business Legacy free accounts. If a Google Apps tenant is a Google Apps for Business Legacy free account, end user credentials must be used. Refer to KB005124 for more information on migrating with end user credentials.
Make sure there are no spaces before or after the scope entry. This will cause the authorization to fail.
Set the Advanced Option to send a notification to end users after the migration pass completes.