The screen won't unlock, Apple Pay won't go through, and the phone seems to be hinting: we don't know each other any more. Until recently this was a known bug — Face ID on the new "Pro" models could drop out after an update. Apple was quick to react and officially fixed the problem in iOS 27.0.1.
So if your phone has suddenly stopped recognising its owner, the first thing to check is the system version. The path is simple: Settings → General → Software Update. If you're on anything older than 27.0.1, download it, install it, don't put it off. In most cases Face ID comes back to life after that, and no further magic is required. The update quietly patches the software that Apple had managed to break.
Didn't help the first time? Next on the list is re-teaching your face. Open Settings → Face ID & Passcode → Reset Face ID, then set it up again. At this step it's important to take off thick-rimmed glasses, step away from a window with bright sun, and turn your head slowly, like an owl that's in no hurry. A fresh face scan often solves the problem in a minute.
The third step is a restart. Just switch it off, wait half a minute and switch it on. It sounds like the kind of advice that goes "try taking it out and putting it back in", but it's exactly what catches the small software snags left over after an update.
If after all this the iPhone is still ignoring your face, the problem is most likely in the hardware. This is no longer software that can be fixed with an update: either the TrueDepth camera or the Face ID module needs professional diagnostics. At IRON SERVICE we know how to tell one from the other: we connect it, test it, find the culprit — and tell you exactly what needs fixing. Sometimes the solution is simple, sometimes it's more serious, but you certainly won't be hunting for the cause with your eyes closed.