What you’re sending isn’t a valid HTTP 1.1 request. (It’s being parsed as HTTP 0.9, which has been obsolete for decades, and which our servers generally do not support.) An HTTP 1.1 request must include the version number, as well as the Host header; it’s also generally a good idea to include a User-Agent, e.g.
GET / HTTP/1.1
Don’t forget the blank line at the end of the request! It’s required to let the server know when you’re done sending your request.