SB2209 not found on CANBus

I can't get my SB2209 working over CAN, need help:

I have an Octopus MCU with Klipper, which is connected via USB to CAN Bridge with my PI.
"~/klippy-env/bin/python ~/klipper/scripts/canbus_query.py can0" gives me the uuid of my Octopus MCU (no SB2209 connected at this time).

Then i flashed Klipper on the SB2209 via USB - according to the Documentation, STM32G0B1, 8Mhz, PB0/PB1, 1000000Baud. Flashing went fine ("File downloaded succesfully"). I removed the 5V jumper and set the CANBus Terminator Jumper R120 on the SB2209, connected it to the Octopus via RJ11.

But it's not found on the CanBus, no matter what i try (flashed several times now, checked wiring of the RJ11, etc..).
"~/klippy-env/bin/python ~/klipper/scripts/canbus_query.py can0" still gives me only one uuid - the one from my OctopusBoard

LEDs on the SB2209 are both on (green and red). Not sure what this means, can't find it on the documentation.

Start with scripts/canbus_query.py and the documented SB2209 CAN configuration, then review the reported wiring, jumpers, baud rate, and MCU settings. Reproduce the query on can0 and use the expected result—an additional SB2209 UUID appearing alongside the Octopus UUID—to determine whether the issue is resolved.

Written by the indexing model from the issue text.