"WebSocket connection failed" error

The online demo was working fine up until a few days ago but it’s giving me “WebSocket connection failed” error now.
Has something changed?
I would appreciate it if you can explain what’s causing it so that I better understand what’s going on.


It’s working now.
Thanks to those who helped, silently. ^^

I was trying to setup a local server myself and was having a similar problem.
I believe I got all the certificates set up correctly but the web socket cannot connect.
It could be a simple configuration problem. I tried many things but still having the issue.
I wish there is some checklist for debugging for the new user.