I am using this plugin https://wordpress.org/plugins/authorizenet-woocommerce-addon/ to integrate authorize.net with woocommerce on Wordpress.
It works fine with the sandbox but when I use it with the live mode and live API key and live Transaction Key I get this error "Country must be a valid three-character value if specified.". I am using mastercard and visa.
As I say it works fine with sandbox so I assume it is a setting in the account setup?
Thanks for any help!
It seems this error is to do with using woocommerce with EvoSnap processor.
I got around this error by editing /wp-content/plugins/woocommerce/i18n/countries.php and changed UK to GBR.
I hope this helps someone!