Bluetooth API for Nuki Box

Hi Nuki Team,
I want to connect to the Nuki Box via Bluetooth and open a door when no internet connection is available. This is possible in the Nuki app but unfortunately, there is no documentation on the implementation of it.
I’m already able to connect to an Opener when it is in pairing mode, but since the Box has no pairing mode and should be used by unknown devices that procedure is not applyable in that scenario, or is it?

What exactly are the steps to connect to the Box (with a prevouisly generated key) and trigger the opening or closing mechanism?

Thank you,