Symfony4 - 'app/config/config.yml' is missing?
As Arnold Richmon indicated. Also, in the fos_user.yaml file you need to add config options as:
fos_user: db_driver: orm # other valid values are 'mongodb' and 'couchdb' firewall_name: main user_class: App\Entity\YourUserEntityClass from_email: address: "youremail@yourdomain.whatever" sender_name: "yoursendername"