I think you mean "can't see the mini when I try to connect via Airplay from/on any of my IOS devices" and by "all working fine" I think you mean that playing/streaming other services works on the mini so a working wifi (internet) connection is already in place. Is the wifi connection to a static device like a router on a home network or maybe the mini's wifi is connected via one of the i-devices?
Configuring/using the Apple Home app is not necessary for it to appear as an Airplay endpoint, that should just work (does for other users/me) that's "only" a cool way of integrating a WiiM into a smart home setup and to operate it using Siri.