Fatal error: Uncaught Error: Call to undefined function Inpsyde\Zettle\add_action() in /var/www/html1/wp-content/plugins/zettle-pos-integration/zettle-pos-integration.php:115 Stack trace: #0 /var/www/html1/wp-content/plugins/zettle-pos-integration/zettle-pos-integration.php(157): {closure:/var/www/html1/wp-content/plugins/zettle-pos-integration/zettle-pos-integration.php:33}() #1 {main} thrown in /var/www/html1/wp-content/plugins/zettle-pos-integration/zettle-pos-integration.php on line 115