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

[MarcoI]

Thank you very much Francis!!! Your indications solved this problem:
with vue.config.js : 

// vue.config.js
module.exports = {
  // options...
  publicPath: '',
  devServer: {
    host: '0.0.0.0',
    port: 8080,
    public: 'ggc.world'
  },
}

now it works fine:
https://drive.google.com/open?id=1PUctgdYLoVmJRvYyG040BFNGOev2yhRX

The previous problem looked similar but I guess it was somewhat different,
because it disappeared once moving from Server Edition to Desktop edition of
Ubuntu 18.04.4 .

Thank you very much again for your kind help.

Marco

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,286850,287000#msg-287000