protected function addBilling(array $params, array $options)
    {
        if ($address = Arr::get($options, 'billing_address')) {
            $params['payer']['payer_info']['billing_address'] = [
                'line1'        => Arr::get($address, 'address1', ''),
                'line2'        => Arr::get($address, 'address2', ''),
                'city'         => Arr::get($address, 'city', ''),
                'country_code' => Arr::get($address, 'country', ''),
                'postal_code'  => Arr::get($address, 'zip', ''),
                'state'        => Arr::get($address, 'state', ''),
            ];
        }

        return $params;
    }