Notice: Undefined index: email in /var/www/klaviyo.levlup.de/subscribe.php on line 8

Fatal error: Uncaught KlaviyoException: You must identify a user by email in /var/www/klaviyo.levlup.de/vendor/klaviyo.php:61 Stack trace: #0 /var/www/klaviyo.levlup.de/subscribe.php(8): Klaviyo->subscribe() #1 {main} thrown in /var/www/klaviyo.levlup.de/vendor/klaviyo.php on line 61