[ USD50 ] Apache configuration for reverse proxy for socket.io

I am a web developer.
I developed a kind of Chat App by using CodeIgniter3 (PHP), and Socket.io(Node.js).
I am using Digital Ocean Droplet for the app server.
I am using Digital Ocean's Load Balancer, and connect it to 2 app servers.
I am using Couldflare WAF & SSL.
The app server is using Apache/Ubuntu.

I setup Socket.io server inside the apache server.
I start socket.io server by the command "node server.js".

Users access to the site via port 443 (SSL).
For the socket.io, I use "port 8443" , because 443 cannot be used.
But some user cannot use 8443, because their security software block it. Then they can't use my Chat app.

I heard that reverse proxy might be solution for this.
https://socket.io/docs/v4/reverse-proxy/#Apache-HTTPD
https://stackoverflow.com/questions/48970876/running-socket-io-over-apache-reverse-proxy

But I tried many times by referring to the online articles above, but socket.io cannot be established at all after the configuration.

I changed the configuration on this config file.
/etc/apache2/sites-available/default-ssl.conf

(Of cause, I did sudo a2ensite default-ssl.conf , and restarted apache to make the new setting effective.)

I am looking for an expert of apache setting and socket.io application. I need your help until the socket.io works even for those who block port 8443.

I will pay you USD50 via freelancer, when I can configure properly based on your advice.