When I activated the ATUM plugin for the first time I received some warnings (below). We think the last three are just PHP shortcomings, but wanted to share them all, as the first one may actually be a bug.
Warning: foreach() argument must be of type array|object, bool given in /usr/local/www/wordpress/wp-content/plugins/atum-stock-manager-for-woocommerce/classes/Addons/Addons.php on line 599
Warning: Cannot modify header information - headers already sent by (output started at /usr/local/www/wordpress/wp-content/plugins/atum-stock-manager-for-woocommerce/classes/Addons/Addons.php:599) in /usr/local/www/wordpress/wp-admin/includes/misc.php on line 1416
Warning: Cannot modify header information - headers already sent by (output started at /usr/local/www/wordpress/wp-content/plugins/atum-stock-manager-for-woocommerce/classes/Addons/Addons.php:599) in /usr/local/www/wordpress/wp-includes/functions.php on line 6865
Warning: Cannot modify header information - headers already sent by (output started at /usr/local/www/wordpress/wp-content/plugins/atum-stock-manager-for-woocommerce/classes/Addons/Addons.php:599) in /usr/local/www/wordpress/wp-admin/admin-header.php on line 9