You’re probably here because you just got a new HomeKey lock, or a new iPhone, or a new Apple Watch.
Or you’ve just reconfigured them so they’re like new.
But when you bring your device close, it flashes, but doesn’t open the device.
The fix is to simply hold it close for longer—maybe like 5-7 seconds or so.
I’m not sure what the technical mechanism is, but it’s basically like an initial setup phase for the lock/device learning the new Watch or iPhone.
Subsequent taps should then work like normal.