The “legacy” method refers to the Table Rate shipping method that existed before WooCommerce added shipping zones to the core plugin. In order to provide the best compatibility moving forward, this plugin also switched to the new shipping API that included these shipping zones. Table Rate Shipping for WooCommerce version 4.0 was released on April 14th, 2017 effectively retiring the legacy method. There have been numerous WooCommerce updates since that date, and over that time the legacy method lost compatibility and is known to cause error messages such as:
PHP Warning: A non-numeric value encountered in /wp-content/plugins/woocommerce-table-rate-shipping/deprecated/woocommerce-table-rate-shipping.php on line 388 PHP Warning: array_unique() expects parameter 1 to be array, null given in /wp-content/plugins/woocommerce-table-rate-shipping/deprecated/woocommerce-table-rate-shipping.php on line 2271
It is highly recommended that you cease using this method if it is still active. Some of these messages may still appear even when the method is disabled (for users prior to the Table Rate 4.2 update). Not sure if you are using the legacy method? The legacy method is accessed from the sub-menu of the ‘Shipping’ tab in your WooCommerce settings.
The legacy method is only available to users who have used this method in the past, prior to the 4.0 update. New users will not be able to see this link. To remove this method and cease the PHP warnings it causes, upgrade your Table Rate Shipping plugin to 4.2. Then navigate to this page, uncheck the Enable / DIsable checkbox, and save your settings. Completing this will stop the old method from loading and you will be redirected to the Shipping Zones page where your new Table Rate methods are located.
If you are still actively using this method, make sure to reconfigure your shipping in the new method before proceeding. The following articles will help you get started: