Hello, thank you for your question. 

To address your issue, the problem likely arises because the BigQuery connector expects a JSON credentials file or an environment variable pointing to it. Using a Databricks Secret directly requires extra steps. Here's how you can resolve it:

• Retrieve the JSON credentials from the Databricks Secret as a raw string, avoiding Base64 encoding. Ensure the JSON is passed exactly as it was stored in the secret.
• Dynamically create a temporary file in your environment to store the credentials. Use a method to write the JSON credentials to a file and set the GOOGLE_APPLICATION_CREDENTIALS environment variable to the path of this file.
• Confirm that your Spark session has the required configurations set for BigQuery, including the temporary GCS bucket and parent project. Ensure the service account in your credentials has permissions for both the BigQuery table and the GCS bucket.
• Double-check that your temporary GCS bucket is properly configured and accessible by the service account, as write operations often rely on this intermediate storage.

If these steps don't resolve the issue, feel free to share additional details for further assistance.