-8 error while logging to ZAPP

Getting -8 error while logging to ZAPP…
What could be the issue?

https://help.zscaler.com/z-app/zscaler-app-errors

  • 8 = This error occurs when Zscaler Client Connector is unable to connect to the cloud.

Could you please share the resolution steps for the same?
Are there any IPs which needs to be whitelisted from my firewall to allow ZAPP connect to the ZEN?