Captive portal using wifidog on openwrt

I work on a captive portal wifidog on openwrt using tplink tl-mr3020.
the installation of wifidog went well but when debug it, it seems like it couldn't create a web server on the ip adress of the openwrt and it shows the error below:

could not create web server : addess already in use

I linked the openwrt router that has as ip address as to wifi router that has

I couldn't detect the error.

please more info openwrt version and wifidog version. where you use webserver on the router or external server ?