
This how-to explains how to add a new Zigbee device to the coordinator and get its widgets in Domoticz.
A Zigbee network is encrypted. To pair a device, the network is opened for a short time (permit to join): the new device joins, receives the network key, and can then talk to the coordinator once the network is closed again.
Once the device has joined, the plugin interviews it (endpoints, clusters, model), configures it, and creates the matching widgets in Domoticz.
The plugin creates the widgets itself, but Domoticz refuses any new widget while its own Accept new Hardware Devices setting is off: the Domoticz log then shows Device creation failed, Domoticz settings prevent accepting new devices.
In Domoticz, go to Setup > Settings > System and check that Accept new Hardware Devices is enabled (or click Allow for 5 minutes before pairing).

This Domoticz setting is not the Accept new hardware switch of the plugin WebUI menu bar: the WebUI switch opens the Zigbee network for pairing for 4 minutes, the Domoticz setting allows the widgets to be created.
The new widgets are listed in Domoticz under Setup > Devices (the last ones). Click the green arrow of the ones you want to use to add them to the dashboards.
More advice in Build a Zigbee network.
All the methods are on the Admin > Provisionning page of the WebUI (see WebUI Admin):

There are three ways to pair:
In the Pairing a new device with the assistant panel, click Pairing. The network is open for 4 minutes.

When the device has joined, the assistant shows what the plugin learned about it, and the widgets created.

The assistant only shows devices joining for the first time. A device that was already known to the plugin (re-paired) doesn’t appear: check the Domoticz log to see that it has rejoined.
If nothing happens after 2 minutes:
This method opens the network without the assistant; you follow the pairing in the Domoticz log (Setup > Log, you can filter on the plugin name).
In the Pairing a new device for a period of time panel, click 4 minutes. The Accept new hardware switch of the WebUI menu bar does the same.

Click Stop to close the network before the 4 minutes are over.
By default a new device joins through whichever router or coordinator answers it. You can make it join through a router you choose, for example a device far from the coordinator.
The device is only forced to join through that router: later, the network may route its messages another way, and you have no control over that.
In the Pairing a new device on a router panel, select the router.

After a device has joined, the network may be opened on all the routers. To pair another device through that specific router only, start again from step 1.
When a device is paired, the plugin creates one widget per function of the device. For example an Aqara temperature sensor gets 5 widgets: Temperature, Humidity, Pressure, Temperature + Humidity, and Temperature + Humidity + Pressure.
You can delete the widgets you don’t need in Domoticz. A deleted widget is not created again on its own. To get it back:
Don’t delete all the widgets of a device unless you want to remove it: deleting the last widget removes the device from the network.
If you factory-reset a device that is already paired, prepare the plugin first: on the Admin > Provisionning page, in the Preparing device for full reset panel, select the device and click Reset mode.
The plugin forgets what it learned about the device (bindings, reporting configuration…). At its next pairing, the device goes through the full discovery and configuration again, as if it were paired for the first time. Its existing widgets are kept.