VM is running but I can't see an

I have a strange problem. I can instantiate a VM and can even ping or ssh to the VM but the VM does not boot in the web browser. Instead, I get a TUNNEL_ERROR. I am using VNC.

What might be the problem and how can I fix it.? Any help is greatly appreciated.

Use following link
https://docs.opennebula.io/6.0/installation_and_configuration/frontend_installation/install.html#frontend-fw

FireEdge

OneGate (Optional)

OneFlow (Optional)

following setting change it should work vnc