If your inspector is running via an on-premises agent, verify that you can successfully log into your Synology NAS device via the application portal from the machine on which the agent is installed.

Verify that you're able to login to the application portal using the hostname and port you specified in the inspector template:

Using the browser of your choice, attempt to reach your device's application portal by entering your device's hostname in the address bar, followed by the HTTPS port, e.g. <hostname>:<port>