400 bad request error after sending CONNECT request with netty (java)

[rocksamrocks]

Hi
I'm using netty to send a CONNECT request. It's sending the request to openresty which in turn is redirecting it to the server. But I get a 400 bad request error if I do this, with the nginx error.log saying "client sent invalid request while reading client request line, client: 127.0.0.1, server: , request: "CONNECT / HTTP/1.1""

Here's an idea of what my nginx.conf looks like:
stream {
server {
listen 6443 ssl;
.
.
.
http {
upstream {
...}
map { ... }

server {
listen 443 ssl;
...
location / {
...
proxy_pass http://upstream;
...

Now I think the nginx configuration as well as the netty java code is fine because I tested it out with nginx-1.16.1
Right now I'm testing this out with openresty-1.25.3.1 where I get the 400 error.

What could be the reason?

Thanks