Hi,
i use Zerotier for some time to distribute ipv6 access on my devices. In the past i had issues assigning global IPv6 Adresses because i didnt know about “allowGlobal”. So i used radvd for ip and route distribution. Sometimes radvd ist quiet slow and it takes up to 10 min. for clients to pickup an ipv6 so i searched how to use Zerotier Central to assign IPv6 IPs and found that i need AllowGlobal and allowDefault.
Today i renumbered my Subnet and i give Zerotier clients IPv6 adresses, set route for ::0/0 to my Router and set allowglobal and allowdefault on all my clients, so far no success. Clients get IPv6 IPs but a non working route. I compared the routes from my new and my old radvd apporach and found out that the default route has to be the fe80:… of the Router, so i put that in Zerotier Central as route for ::0/0 but no success, it doesnt get distributed to the zerotier clients 
Settings route by hand after starting zerotier with ip -6 route add default via fe80:… (ip of my router) dev zt… works, clients can now reach the internet via ipv6.
Is this approach wrong? how is the correct way to distribute ipv6 routes to zerotier clients?