Issue pairing master-slave nicenano v2

Hi there! I just received and mounted a corne with nicenano v2. The problem: the slave does not appear to be pairing to the master. It is not working at all (see video). See also pics from the soldering. This far we tried: - Mounting the master/left firmware on both halves. Both work, and both connect to the laptop via bluetooth. But the right or slave halves don’t. - mounted different nicenanos from another keyboard to the pcb. We understand the problem is not the PCB, because those nicenanos from the other keyboard work. - the new nicenanos had the same problem in the working keyboard’s PCB. - we tried the firmware from the old keyboard, which works with the old nicenanos, with the new ones. Same problem. - We managed to type 2 characters at some point, but inmediatly disconected. It was connected to a power supply via the usb. So it should not be far from working. - We reseted the firmware multiple times. We don’t know what else to try 🥲