Purchase Order Plugin for v 2.1

[JG64]

I have made an attempt to update the /includes/modules/payment/purchaseorders.php code to work with ZenCart v2.1 and PHP v8.3. Here is what I have come up with:

 <?php
if (!defined('TABLE_CUSTOMERS')) {
  define('TABLE_CUSTOMERS', 'zen_customers');
}

if (!defined('TABLE_GROUP_PRICING')) {
  define('TABLE_GROUP_PRICING', 'zen_group_pricing');
}

class purchaseorder extends base {
  public $code;
  public $title;
  public $description;
  public $enabled;
  public $sort_order;
  public $order_status;

  public function __construct() {
    global $order;

    $this->code = 'purchaseorder';
    $this->title = MODULE_PAYMENT_PURCHASEORDER_TEXT_TITLE;
    $this->description = MODULE_PAYMENT_PURCHASEORDER_TEXT_DESCRIPTION;
    $this->sort_order = defined('MODULE_PAYMENT_PURCHASEORDER_SORT_ORDER') ? MODULE_PAYMENT_PURCHASEORDER_SORT_ORDER : 0;
    $this->enabled = (defined('MODULE_PAYMENT_PURCHASEORDER_STATUS') && MODULE_PAYMENT_PURCHASEORDER_STATUS == 'True');

    if ((int)MODULE_PAYMENT_PURCHASEORDER_ORDER_STATUS_ID > 0) {
      $this->order_status = MODULE_PAYMENT_PURCHASEORDER_ORDER_STATUS_ID;
    }
  }

  public function update_status() {
    global $order;

    if (($this->enabled == true) && ((int)MODULE_PAYMENT_PURCHASEORDER_ZONE > 0)) {
      $check_flag = false;
      $check_query = zen_db_query("SELECT zone_id FROM " . TABLE_ZONES_TO_GEO_ZONES . " WHERE geo_zone_id = '" . MODULE_PAYMENT_PURCHASEORDER_ZONE . "' AND zone_country_id = '" . $order->billing['country']['id'] . "' ORDER BY zone_id");
      while ($check = zen_db_fetch_array($check_query)) {
        if ($check['zone_id'] < 1) {
          $check_flag = true;
          break;
        } elseif ($check['zone_id'] == $order->billing['zone_id']) {
          $check_flag = true;
          break;
        }
      }

      if ($check_flag == false) {
        $this->enabled = false;
      }
    }
  }

  public function javascript_validation() {
    return false;
  }

  public function selection() {
    return array('id' => $this->code,
                 'module' => $this->title);
  }

  public function pre_confirmation_check() {
    return false;
  }

  public function confirmation() {
    return array('title' => $this->title);
  }

  public function process_button() {
    return false;
  }

  public function before_process() {
    return false;
  }

  public function after_process() {
    return false;
  }

  public function get_error() {
    return false;
  }

  public function check() {
    if (!isset($this->_check)) {
      $check_query = zen_db_query("SELECT configuration_value FROM " . TABLE_CONFIGURATION . " WHERE configuration_key = 'MODULE_PAYMENT_PURCHASEORDER_STATUS'");
      $this->_check = zen_db_num_rows($check_query);
    }
    return $this->_check;
  }

  public function install() {
    zen_db_query("INSERT INTO " . TABLE_CONFIGURATION . " (configuration_title, configuration_key, configuration_value, configuration_description, configuration_group_id, sort_order, set_function, date_added) VALUES ('Enable Purchase Order Module', 'MODULE_PAYMENT_PURCHASEORDER_STATUS', 'True', 'Do you want to accept purchase order payments?', '6', '0', 'zen_cfg_select_option(array(\'True\', \'False\'), ', now())");
    zen_db_query("INSERT INTO " . TABLE_CONFIGURATION . " (configuration_title, configuration_key, configuration_value, configuration_description, configuration_group_id, sort_order, date_added) VALUES ('Sort order of display.', 'MODULE_PAYMENT_PURCHASEORDER_SORT_ORDER', '0', 'Sort order of display. Lowest is displayed first.', '6', '0', now())");
    zen_db_query("INSERT INTO " . TABLE_CONFIGURATION . " (configuration_title, configuration_key, configuration_value, configuration_description, configuration_group_id, sort_order, use_function, set_function, date_added) VALUES ('Payment Zone', 'MODULE_PAYMENT_PURCHASEORDER_ZONE', '0', 'If a zone is selected, only enable this payment method for that zone.', '6', '2', 'zen_get_zone_class_title', 'zen_cfg_pull_down_zone_classes(', now())");
    zen_db_query("INSERT INTO " . TABLE_CONFIGURATION . " (configuration_title, configuration_key, configuration_value, configuration_description, configuration_group_id, sort_order, use_function, set_function, date_added) VALUES ('Set Order Status', 'MODULE_PAYMENT_PURCHASEORDER_ORDER_STATUS_ID', '0', 'Set the status of orders made with this payment module to this value', '6', '0', 'zen_get_order_status_name', 'zen_cfg_pull_down_order_statuses(', now())");
  }

  public function remove() {
    zen_db_query("DELETE FROM " . TABLE_CONFIGURATION . " WHERE configuration_key in ('MODULE_PAYMENT_PURCHASEORDER_STATUS', 'MODULE_PAYMENT_PURCHASEORDER_SORT_ORDER', 'MODULE_PAYMENT_PURCHASEORDER_ZONE', 'MODULE_PAYMENT_PURCHASEORDER_ORDER_STATUS_ID')");
  }

  public function keys() {
    return array('MODULE_PAYMENT_PURCHASEORDER_STATUS', 'MODULE_PAYMENT_PURCHASEORDER_SORT_ORDER', 'MODULE_PAYMENT_PURCHASEORDER_ZONE', 'MODULE_PAYMENT_PURCHASEORDER_ORDER_STATUS_ID');
  }
}

When I uploaded it to the test store and logged in to the admin area - 'modules/payments' does not show the plugin, so I am unable to install it. Any suggestions on how to fix the code would be greatly appreciated. I would like to get this plugin upgraded to v2.1 for all.