Hello,
This error usually occurs when you have a poor connection to the game server. There are several things you can do to try to fix this error.

In order of severity, I would suggest trying
Clear the browser/client cache
Flush the DNS cache
Reboot the PC/device
Try a different device
Try a VPN program.

If you are trying a VPN, keep in mind that you may need to try several different VPNs to make it work to route you around the problem.