Ubuntu + Nginx: directory index of "/var/www/app/my-app/" is forbidden
The error is due to the $uri/ part of the try_files clause which instructs nginx to serve the content of the directory /var/www/app/my-app/. Directory listing is forbidden by default, you can enable it by adding autoindex on; to the location.
It's seems like the file /var/www/app/my-app/public/index.php does not exist.