Permission issues for BigQuery / Ads Transfer Service

[Ethan Lyon]

I've followed the instructions here: https://cloud.google.com/bigquery/docs/working-with-transfers. 

BigQuery is enabled, I'm the project  and the AdWords MCC owner. "Exclude removed/disabled items" is selected and I still can't get access to data that's owned by the account ID.

I've logged in and authenticated on the Transfers page and am receiving the error:

"Error in Update credentials: The caller does not have permission"

And I'm also getting this error when running backfill jobs:

generic::invalid_argument: Error while processing report for table 'PlacementStats' for account id xxx-xxx-xxxx. Http(400) Bad Request; <?xml version="1.0" encoding="UTF-8" standalone="yes"?><reportDownloadError><ApiError><type>AuthorizationError.USER_PERMISSION_DENIED</type><trigg...

One weird thing that's happening is I cannot enable the Ads API on my Google Cloud project. I enabled it via the cmd but the page won't load in the API section of the GCP console.

Any help would be greatly appreciated!