Permissions for grantGoogleRoleToUser

Hello, I'm trying to make modifications to the underlying Google project for a Firecloud billing project. I am the owner of the billing account on Google, and the project on Firecloud, so I figured I would also have ownership of the Google project. After reading your docs, I found the grantGoogleRoleToUser endpoint, and thought that I would be able to grant myself permissions to the Google project. However, when I tried the command to grant myself "Owner", the command failed saying that I must be project Owner:

In [21]: fc.__get('me', root_url="https://api.firecloud.org/").json()
Out[21]: 
{'enabled': {'allUsersGroup': True, 'google': True, 'ldap': True},
 'userInfo': {'userEmail': 'agraubert@wustl.edu',
  'userSubjectId': '107298085759454757409'}}

In [22]: fc.__put('billing/graubert-rnaseqc-trial/googleRole/Owner/agraubert@wustl.edu').json()
Out[22]: 
{'causes': [],
 'message': 'You must be a project owner.',
 'source': 'rawls',
 'stackTrace': [],
 'statusCode': 403,
 'timestamp': 1540332396202}

If that's the case, who is the desired user of this command? How would I go about gaining access to the Google project for a Firecloud billing project that I own?

Any help would be appreciated

For reference, the Firecloud/Google account I'm using for this is: agraubert@wustl.edu
and the Google project/Firecloud billing project is: graubert-rnaseq-trial

Thanks!