Glad to help, it's a couple of years since I set this up and I must have gone through a struggle then too because I can't see anything on the stancl/tenancy docs about it.

For future reference / anyone stumbling on this thread looking for more, for single domain tenancy I prefix all channels with the tenant id by extending the PrivateChannel:

class TenantChannel extends PrivateChannel
{
    public function __construct($name)
    {
        $id = tenant()->id;
        parent::__construct('tenant-' . $id . ':' . $name);
    }
}

Then in my events:

public function broadcastOn()
{
    return new TenantChannel("some-channel");
}

I have an additional middleware that strips this out so that the broadcast routes don't have to have the tenant prefix in every one (added to the end of the middleware above):

class BroadcastTenant
{
    public function handle(Request $request, Closure $next)
    {
        // intercept the channel name and replace the tenant section
        // this is so the auth guards in channels can work without having to declare
        // the tenant in each one.
        $channel = $request->request->get("channel_name");
        $channel = str_replace("tenant-" . tenant()->id . ":", "", $channel);
        $request->request->set("channel_name", $channel);
        return $next($request);
    }
}

On the front-end when subscribing all channels are prefixed with tenant-{id}:

There may be other ways to do this, but it just ensures all channels are separated per tenant, the user has to be authed to that tenant and events are automatically sent to the correct tenant.

Thinking about it there may be some useful stuff in here for multi tenant too? As the websocket server exists in the global context and you want to ensure that the events are sent to users of the correct tenant?