How to find the IP address of an iOS device
On the master, go to settings->Wifi.
Click on the i (info button) to the right of the current wifi.
Remember the IP address.
Then on the slave type: http:IP_ADDRESS:8080/
Real world scenario:
On iPhone as master, IP address is 192.168.2.159
Type in: http://192.168.2.159:8080/
for the slave.