INVALID_GRANT on n8n: invalid_grant: Token has been expired or revoked — Root cause: This error occurs when the Google Cloud application associated with the n8n OAuth2 credential is left in 'Testing' mode. In Testing mode, Google enforces a strict security rule where refresh tokens automatically expire and are revoked after exactly 7 days, causing the n8n workflow to fail. — If the error persists after moving the app to Production and re-authenticating, verify that your n8n instance can reach the Google OAuth endpoints without firewall interference. For enterprise environments with strict security policies, consider switching from OAuth2 to a Google Service Account credential instead.