The client is unable to verify that the server is Elasticsearch due to an unsuccessful product check call. Some functionality may not be compatible if the server is running an unsupported product

[stevejgordon (Steve Gordon)]

The 7.16 client performs a pre-flight GET request to the root URL of the server before the first request. This is the one which appears to be failing due to a 404 response. We need to try to determine why that is and the client host can reach that URL.