Web Storage

Web storage is used to send images and files received by Spectrum 2 to end user. When new image or file is downloaded from the 3rd-party network, it is stored into service.web_directory directory and the link to that file, based on service.web_url, is sent to the user.

That means that you should configure the web-server on the machine where you run Spectrum 2 to serve service.web_directory.

If you for example use httpd, you can configure service.web_directory=/var/www/html/spectrum2. In that case, the matching service.web_url value will be service.web_url=http://domain.tld/spectrum2.

Security

You should not configure the webserver to allow listing files in the service.web_directory.