I spent a day to figure out that Google Cloud project just needed a Billing Account linked to it. See my reply on this post: Vertex AI LangChain Agent fails ('asyncIterator' error) when Postgres Chat Memory is connected
You may or may not have the same root cause, but it is likely just that “something connected” is sending a normal error code, and n8n node can’t handle normal error codes, so it bugs out and makes its own unrelated error which tricks you to look for unrelated issues/troubleshooting.