public function setGlobalVar($variable, $value = null)
    {
        $uri = 'asterisk/variable';

        try {
            $this->client->getEndpoint()->post($uri, [
                'form_params' => [
                    'variable' => $variable,
                    'value' => $value
                ]
            ]);
        } catch (RequestException $e) {
            $this->processRequestException($e);
        }
    }