Wirelessly debug Safari web app running on iOS using Safari on macOS
Follow the instructions below one by one:


On your iOS device, go to Settings app → Safari → Advanced and enable the switch for Web Inspector.





On macOS, launch Safari and in the Menu bar, go to Preferences → Advanced and check Show Develop menu in menu bar.





You will need to physically connect your iOS device to Mac mini using the Lightning cable once.
Once the iOS device is connected, in Safari menu on macOS, enable Develop → Your device name → Connect via Network.
Unplug the cable and check whether Develop → Your device name shows up in Safari on macOS.
Safari app needs to be running and frontmost on your iOS device for it to appear under Develop menu in Safari on macOS.


The above configuration is demonstrated on devices running macOS High Sierra 10.13.6 and iOS 11.4.1 (latest version at the time of writing).