net::ERR_CONNECTION_REFUSED . How to correctly configure Nginx with Socket.io?

[MarcoI]

Add-on to the previous email:

using firefox as web browser, I get this error message:
https://drive.google.com/open?id=1l6USIHrbHl6kBcQtormXplOgx0J653ko

  "Cross-Origin Request Blocked: The Same Origin Policy disallows reading
the remote resource at https://localhost/sockjs-node/info?t=1580304400023.
(Reason: CORS request did not succeed)."

Looking at Mozilla Developer explanation:

https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS/Errors/CORSDidNotSucceed?utm_source=devtools&utm_medium=firefox-cors-errors&utm_campaign=default

"What went wrong?

The HTTP request which makes use of CORS failed because the HTTP connection
failed at either the network or protocol level. The error is not directly
related to CORS, but is a fundamental network error of some kind.

In many cases, it is caused by a browser plugin (e.g. an ad blocker or
privacy protector) blocking the request.

Other possible causes include:

    Trying to access an https resource that has an invalid certificate will
cause this error.
    Trying to access an http resource from a page with an https origin will
also cause this error.
    As of Firefox 68, https pages are not permitted to access
http://localhost, although this may be changed by Bug 1488740.
    The server did not respond to the actual request (even if it responded
to the Preflight request). One scenario might be an HTTP service being
developed that panicked without returning any data.
"

Checked the TLS Certificates with https://www.digicert.com/help/ :
and the result is:
" TLS Certificate has not been revoked. 
  TLS Certificate expires soon. The primary TLS Certificate expires on
February 28, 2020 (30 days remaining)
  Certificate Name matches ggc.world
  TLS Certificate is correctly installed "

So may be my nginx configuration has to be improved.

Looking forward to your kind help.
Marco

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,286850,286851#msg-286851