From tunnel site you have
webconfig:Server IPv4 address:
Server IPv6 address:
Client IPv4 address:
Client IPv6 address:
Routed /48: Allocate
Routed /64:
LAN IPv6 settings
I'd recommend :1 address from Routed /64.Static IPv6 address: *an address from Routed /64*
Netsize (bits of hostpart): 64
Enable router advertisements: yes
If you have 2001:db8:4242:4242::/64 as routed/64, you put 2001:db8:4242:4242::1 in Static IPv6 address
Tunnel IPv6 Setting
And this works for me.Enable IPv6-tunnel: yes
Remote endpoint: the Server IPv4 address
Local IPv6 address: the Client IPv6 address
Netsize (bits of hostpart): 64
Remote IPv6 gateway: the Server IPv6 address
Tunnel MTU: 1280
Tunnel TTL: 64
Also note, that routed/64 is different from client and server ipv6 addresses (took me time to note 1a vs 1b in the third 16-bit group).