DFU response 3 not supported

Hello there,

I'm new to DFU and nordic devices in general and am trying to update the firmware of one of my devices (nRF5) via BLE.

Having that said I use python3.9 and bleak (via dbus). I'm able to get all available services and characteristics but when I'm sending x01x04 (init dfu and C4 parameter `4` for application) to the DFU Control Point Characteristics it returns: x10\x01\x03, the last byte indicates "not supported" - the device itself is in OTA mode.

I have no idea where to start. I can basically update the device using other tools but I really wanted to write my own routine for the update procedure.

Thanks in advance!