BigQuery 400 Error when connecting Google Sheet in Looker

Hi everyone,

I’m hitting a wall with a BigQuery 400 Status Code error while trying to connect a Google Spreadsheet to Looker for a self-service Explore. I’ve gone through the standard troubleshooting steps, but the error persists.

Source: Google Sheet (~6,100 rows, 12 columns).

The Problem:
When attempting to link the sheet, Looker returns: “BigQuery returned a 400 status code when Looker attempted to upload the CSV data.”

What I’ve Verified/Tested:

Permissions: The Looker Service Account has been added as a Viewer to the Google Sheet.

Scopes: The BigQuery connection in Looker Admin settings has the https://www.googleapis.com/auth/drive scope enabled.

CSV vs. Link: If I download the sheet as a CSV and upload it manually, it works perfectly. This confirms the data itself is clean and well-under the 100MB limit.

I have also manually reviewed the column data types.
Has anyone encountered this specifically when the CSV upload works but the Drive sync fails with a 400 error?

Appreciate any insights!