NSA325v2 bricked (no replies)

Hello,
I recently got my hands on an NSA325v2 Zyxel NAS and I wanted to install debian on it.
I followed the various procedures but I think I bricked my NAS.

I tried connecting it via serial UART:
usb adapter: GND RX TX 3.3
NAS: GND [empty] RX TX 3.3

Is this correct?

I tried using kwboot from a Raspberry Pi4 and another linux computer but it only gives me the following log:

sudo ./kwboot -t -B 115200 /dev/ttyAMA0 -b uboot.2023.04-tld-1.nsa325.kwb -p
kwboot version 2024.04-rc3-00001-g0861eab8ec-dirty
Detected kwbimage v0 with NAND boot signature
Patching image boot signature to UART
Sending boot message. Please reboot the target...\

and also

./kwboot -t -B 115200 /dev/ttyUSB0 -b uboot.2017.07-tld-1.nsa325.mtd0.kwb  -p
kwboot version 2025.01-rc1-ge61ea9f2e5d2-dirty
Detected kwbimage v0 with NAND boot signature
Patching image boot signature to UART
Sending boot message. Please reboot the target.../

The nas led behaviour is the following:
when connecting the UART adapter to the computers the blue light and yellow DISK2 light come on
sometimes the SYS led lights up but apparently the NAS reboots and it cycles again.

The behaviour is the same even if I connect my rootfs USB drive.

Am I doing this right?
What should I try next?

Thanks
I am new to all this stuff so I really don't know what I'm doing and would appreciate some help.