The config setting for letting a new device join the Zigbee network is found in Zigbee2MQTT”s configuration.yaml

For security reasons it’s important that permit_join: is set to false.  Otherwise rogue devices are able to join allowing them to send and receive Zigbee traffic.

When you want to add a new device editing this setting manually in the config file is a hassle.

Luckily you can issue this CLI command from any connected computer on the LAN to open the network temporarily:

mosquitto_pub -h <hostname> -t zigbee2mqtt/bridge/request/permit_join -m ‘{“value”: true, “time”: 20}’

This will open the network for 20 seconds, enough time to add your device, and when the 20 seconds have passed the network is secure again.

Just keep an eye that no additional rogue devices are added.