Ni WooForce on "[Plugin: Fedex WooCommerce Shipping Method Plugin] Fatal Error after install"

Hello,
Once FedEx Plugin is installed, I activate it then choose "settings", problem is a white page loads with the following error message:

Fatal error: Call to undefined method WC_Countries::get_countries() in /home/content/p3pnexwpnas02_data03/22/2816322/html/wp-content/plugins/fedex-woocommerce-shipping-method/includes/data-wf-settings.php on line 11

how can I fix this? the plugin has to be deactivated.
thanks

https://wordpress.org/plugins/fedex-woocommerce-shipping-method/

Hi Mixshows,

The issue is related to Woocommerce older version you are using.

Please install the latest version of our plugin to fix this issue.