I am currently setting up an open-source marketing software called Mautic on App Engine Flexible Environment. However, I'm having trouble with connecting the App Engine to the Cloud SQL MySQL database using MySQLi. Mautic is a PHP application built on top of Symfony. I tried using /cloudsql/<instance_connection_name> as the host, but it didn't work.
Does anyone have any experience with deploying Mautic on App Engine or know to address this problem?