Login on your flukso via SSH and edit /etc/config/firewall: set wan input to 'ACCEPT':

  config 'zone'
        option 'name' 'wan'
        option 'input' 'ACCEPT'
        option 'output' 'ACCEPT'
        option 'forward' 'REJECT'
        option 'masq' '1'

Now, all traffic over the WLAN interface is accepted, including access to the internal webservice.