Configure ProxMox/Debian and ZeroTier interfaces to route correctly

Proxmox/Debian and ZeroTier gurus only please. Looking to setup a cluster of hosts with ZeroTier. I have installed ZeroTier and hosts can see each other and ping each other. The ZT interface is not selectable in the ProxMox GUI clustering menus, so I need to add some code to get this to appear. I scoured the ProxMox forum and found the following: - check what is ZT interface name(command line in PMX as root): ifconfig In my case is something like : ztnxxxxxx - edit from command line the /etc/network/interfaces file, and add this snippet: auto vmbr77 iface vmbr77 inet static address [login to view URL] netmask 16 bridge-ports ztnxxxxxx bridge-stp off bridge-fd 0 The [login to view URL] is what IP do you setup in the [login to view URL] Network for your PMX host! I have added the following so that the ZT interface is selectable in the cluster menu and looks like its working, but infact this breaks the interface and it is no longer reachable and hosts can no longer ping each other via their Zerotier addresses. I need someone to work out why the interface breaks when the above code is added to /etc/network/interfaces. The end outcome is to have the ZeroTier interface selectable from the GUI clustering menu, and have the interface work as expected (currently not routing properly).