If your clients are located behind a firewall or proxy server that is blocking access to the SafeConsole Cloud server.
The first option is to update the device to a later device software which features improved proxy support.
Another option is to create a rule in the proxy/firewall which is configured so that all HTTPS (port 443) requests to the SafeConsole Cloud server address are allowed, e.g.:
xxxxx-yyyyy.cloud.safeconsole.com (replace x and y with your unique cloud server address).