BigQuery is the most powerful source but connection errors are common during setup.
Authentication
Need BigQuery Data Viewer and Job User roles. Check IAM in Google Cloud Console. Re-authorize in Looker Studio.
Project Not Found
Select correct Cloud project. Must have billing enabled.
Query Errors
Custom Query must be valid BigQuery SQL. Use backticks only for table names. Use full project.dataset.table paths.
Billing
Suspended billing = failed queries. Check Cloud billing dashboard. Use partitioning to reduce costs. Contact us for BigQuery setup.