Warning: Section @zone[1] (wan) cannot resolve device of network 'wan6'

My flukso is working properly. It runs in wifi mode, I have heart beats and sensor readings are published.

However, I'm trying to make my flukso accessible over Wifi.
Should be easy by following the instrunctions on : https://github.com/flukso/flm02/wiki#configurationlocal-flm-access-via-wifi

However, reloading / restarting the firewall gives me following error:

root@flukso-819523:~# /etc/init.d/firewall reload
Warning: Unable to locate ipset utility, disabling ipset support
Warning: Section @zone[1] (wan) cannot resolve device of network 'wan6'
* Clearing IPv4 filter table
* Clearing IPv4 nat table
* Clearing IPv4 mangle table
* Clearing IPv4 raw table
* Populating IPv4 filter table
* Zone 'lan'
* Zone 'wan'
* Rule 'Allow-DHCP-Renew'
* Rule 'Allow-Ping'
* Rule #5
* Rule #6
* Rule #7
* Rule #8
* Rule #9
* Forward 'lan' -> 'wan'
* Populating IPv4 nat table
* Zone 'lan'
* Zone 'wan'
* Populating IPv4 mangle table
* Zone 'lan'
* Zone 'wan'
* Populating IPv4 raw table
* Zone 'lan'
* Zone 'wan'
* Set tcp_ecn to off
* Set tcp_syncookies to on
* Set tcp_window_scaling to on
root@flukso-819523:~#

Any hints to solve this?

Thanks !