public function create($key, $value) {
        $data = Values::of(array('Key' => $key, 'Value' => $value, ));

        $payload = $this->version->create(
            'POST',
            $this->uri,
            array(),
            $data
        );

        return new VariableInstance(
            $this->version,
            $payload,
            $this->solution['serviceSid'],
            $this->solution['environmentSid']
        );
    }