Matillion seems to expect/require that any data processing on BigQuery is charged to the project where the data is being hosted.
This issue manifests as the following error;
"Exception: Access Denied: Project mr-project: User does not have bigquery.jobs.create permission in project mr-project."
But the service account should be able to perform these queries if it has "bigquery.jobs.create" on a project in GCP, i.e. if the account has somewhere to charge the processing costs, GCP doesn't require it to be the same project as the one hosting the data. It's not a data access restriction, it's a cost of operation restriction.
Can the BigQuery billing project be configured in Matillion?