If I understand you correctly, you are trying to enter local and remote GRE tunnel addresses as hostnames, these should be IP addresses since they will be from a private IP address range, 10.1.1.1 for example. You only need public IP address at the server and the server hostname should only be entered into spoke configuration field Hub address.
You can find example configuration on our wiki page.
It is suggested for remote address on the hub to use %any
The BGP configuration is currently not completely accurate