ah, so its talking to the device and app over serial. In that case what needed to be changed from the original Nostr Signing Device extension / protocol to get this to work?

Also if your intending this to be a first class feature of the passport prime then I would suggest we come up with a new signing protocol that isn't tied to an old ESP32 device.
I would love to have something that could work over bluetooth or USB so that (some) mobile web apps could talk to it.