Problem with Jaadu VNC

I am having trouble connecting to jaadu vnc. I am getting a message saying "connection refused you may have a firewall blocking access".
I have setup port forwarding (5900) and have confirmed with the site "canyouseeme.org" I can connect using homes wifi but when I turn off wifi and connect to the external option it gives me that error message. Has anyone had this issue or know how to correct this? I have emailed jaadu and they can't seem to firgure this out. Would appreciate any feedback for a solution to this problem.

Thanks