Conbee 2 and Zigbee2MQTT (Mosquitto) both use the same ports and affect Firmware connecting - dresden-elektronik/deconz-rest-plugin GitHub Wiki
If your recieving the Firmware - Not Connected issue, chances are you could be running services which are trying to use the same port. One thing to note is that ports 80 and 8080 a used by Conbee2 (possibly others).
You can't have Zigbee2MQTT (z2m) and/or Mosquitto running as active services on your Raspberry PI or you will have issues connecting your Conbee 2 gateway to your Phoscon Software.
To ensure Z2M and Mosquitto aren't running excute the following commands
Remove from Start up Remove from startup boot so they dont auto startup. sudo systemctl disable zigbee2mqtt sudo systemctl disable mosquitto
Stop the services sudo systemctl stop zigbee2mqtt sudo systemctl stop mosquitto
Confirm Services are stopped, check services a stopped now: systemctl status zigbee2mqtt systemctl statys mosquitto