Fatal error: Uncaught Error: Call to undefined function is_checkout() in /usr/local/www/polyplot.de/wp-content/plugins/checkout-fees-for-woocommerce/includes/class-alg-wc-checkout-fees.php:309 Stack trace: #0 /usr/local/www/polyplot.de/wp-includes/class-wp-hook.php(307): Alg_WC_Checkout_Fees->enqueue_checkout_script('') #1 /usr/local/www/polyplot.de/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters(NULL, Array) #2 /usr/local/www/polyplot.de/wp-includes/plugin.php(474): WP_Hook->do_action(Array) #3 /usr/local/www/polyplot.de/wp-includes/script-loader.php(2115): do_action('wp_enqueue_scri...') #4 /usr/local/www/polyplot.de/wp-includes/class-wp-hook.php(307): wp_enqueue_scripts('') #5 /usr/local/www/polyplot.de/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters(NULL, Array) #6 /usr/local/www/polyplot.de/wp-includes/plugin.php(474): WP_Hook->do_action(Array) #7 /usr/local/www/polyplot.de/wp-includes/general-template.php(3042): do_action('wp_head') #8 /usr/local/www/polyplot.de/wp-content/themes/storefront/hea in /usr/local/www/polyplot.de/wp-content/plugins/checkout-fees-for-woocommerce/includes/class-alg-wc-checkout-fees.php on line 309