I've tried several times to install the wireless update for 12 June 2018, but each time I tried I get an error.
Have you installed rooted Android? The OTA update doesn't work with that; you need to reflash it.
(Rumour has it that once that update's installed, any
future OTA updates will work — but of course we can't tell yet.)
I ordered mine on IndieGoGo so I'm assuming that I have an x25. And I don't see the SIM cards menu. Can I be certain it is an x25?
Only the very first production run (sent out in February) were x25; everything since then (i.e. the majority) has been x27.
On mine (x27), the ‘SIM cards’ menu is the third one in the Settings, between ‘Bluetooth’ and ‘Data usage’.
Another indicator is in the notification bar at the top of the screen: if you see two triangles to the left of the battery icon, then you have two SIM cards (the physical one and an eSIM) and hence an x27; only one indicates an x25.