Bluez Mesh : Send : Get key_index

Question

I'm trying to make a Ble Mesh application using the bluez dbus api.

I have made a provisioner on a linux device and an unprovioned node on an other. When I have successfully provisioned my node with the provisioner, I need to send a message from the provisioner to the node.

For that I call the method void Send(object element_path, uint16 destination, uint16 key_index, dict options, array{byte} data) fom the org.bluez.mesh.Node1 but I got this error :

[org.bluez.mesh.Error.InvalidArgs] Key not found

So my question is : How can I get or generate the key_index value ?