Using ServerSentEvents SSE with nodejs app

I have set up a digital ocean server with openlitespeed + nodejs one click installer.

I want to use server sent events in nodejs with openlitespeed as reverse proxy.

I have another server with nginx + nodejs where server sent events is working fine. But with openlitespeed, I am getting a 503 error.

I have tried max keep alive connections, keep alive connection timeout, cache module off but still get 503 error. The SSE eventsource http request is not even reaching the nodejs server with openlitespeed.

How can I get SSE to work with openlitespeed?