public static function getByCustomAttribute(string $key, string $value): ClientCollection
    {
        // TODO: Determine if this is ALWAYS the case!
        $key = lcfirst($key);

        /** @var ClientCollection $clients */
        $clients = Client::get("", [], [ "customAttributeKey" => $key, "customAttributeValue" => $value ]);
        return new ClientCollection($clients->elements());
    }