Accessing an ipv6 NAT64 connection on my iPad, broadcast from Mac
I did the same a couple of days ago to control my app for ipv6 (even if I didn’t need to do so), you should also switch off WiFi on you router / modem and you need to switch on the airplane mode on you iPad. 
Mind that in the latest version of Xcode your app must be compiled for ipv6 automatically.