Install CONBEE2 on Synology HA docker "Failed to connect"

Hi there, just started with HA coming from Domoticz and trying to install the CONBEE2 on integration ZHA.
I run Home Assistant in Docker on a Synology RS815 with DSM 7.1.1
During install I have to give in the Zigbee radio type, that would be DeCONZ, I presume. After that I need to give in a serial device path.
I’m really stuck there. DSM 7 does not handle serial USB anymore, so I followed this link: Synology: How to Add USB Support on DSM 7 – Marius Hosting
According to my taskmanager, port /dev/ttyACM0 is activated.
When I submit this as path, there comes an error saying “Failed to connect”. Changing Data Control Flow does not help here.
When I check my usb devices with lsusb in Putty I get the following:


So I guess the Conbee is found here under usb2_2
What is the correct path here?

Thanks in advance