pfSense

If you define any "IPv6 Tunnel Network" in TAP mode,
an invalid 'ifconfig-ipv6' option is created in the config file:

ifconfig-ipv6 fc00:1111::2 64

must be:

ifconfig-ipv6 fc00:1111::2/64 fc00:1111::1

error:

Apr 29 13:35:14 pf41 openvpn[25432]: Options error: ifconfig-ipv6 parms 'fc00:1111::2' and '64' must be valid addresses
Apr 29 13:35:14 pf41 openvpn[25432]: Use --help for more information.

from https://openvpn.net/community-resources/reference-manual-for-openvpn-2-4:

–ifconfig-ipv6 ipv6addr/bits ipv6remote
configure IPv6 address ipv6addr/bits on the “tun” device. 
The second parameter is used as route target for –route-ipv6 if no gateway is specified.

–route-ipv6 ipv6addr/bits [gateway] [metric]
setup IPv6 routing in the system to send the specified IPv6 network into OpenVPN’s “tun”. 
The gateway parameter is only used for IPv6 routes across “tap” devices, and if missing, the “ipv6remote” field from –ifconfig-ipv6is used.