protected function buildParams(SmsGatewayMessage $message, $to)
    {
        $optionalFields = array_filter([
            'expires_at' => data_get($message, 'expiresAt'),
            'send_at'    => data_get($message, 'sendAt'),
        ]);

        return array_merge([
            'number'     => $to,
            'message'    => trim($message->content),
        ], $optionalFields);
    }