Just today, I received and made a Corne kit with nice!nanos. However, I can't seem to get it actually working. I've built the default ZMK configuration and tried to flash it to the board. It seems to accept the file, exits bootloader mode and disappears from my file manager. But the blue light just blinks, and I can't type anything with it. I know that isn't much more to go off of than "it doesn't work", but I can't see anything in the docs or elsewhere, and I'm not sure where to look next.
Does it appear to your operating system as a keyboard (when connected via USB)? If it does but you just can't type, check you have the nice!nanos the right way up and/or in the right set of holes (depending on your pcbs, some corne pcbs have multiple possibilities so it's easy to get wrong)