How can I troubleshoot a 'connection refused' error when monitoring a specific service with PRTG?

Troubleshooting involves several steps: 1) Verify the target device's IP address and port are correct in PRTG. 2) Confirm the service is running on the target device using tools like `netstat` or `ss`. 3) Check for firewalls (both on the PRTG server and the target device) blocking the connection on the relevant port. 4) Ensure the target device is reachable via ping. 5) Temporarily disable firewalls for testing purposes (with caution) to isolate the issue. 6) Inspect PRTG's logs for more detailed error information.