Go to `Operations` > `RADIUS` > `Live Logs`
Filter by `Authentication Status` = `Failed`
Filter by `Identity Source` or `Network Device` if needed
Search for the MAC address in the `Username` field using the format `AABB.CCDD.EEFF` or `AA-BB-CC-DD-EE-FF`
Open the failed log entry to view the `Failure Reason`
Check `Details` for `Authentication Method` and `Policy Set`
Go to `Operations` > `RADIUS` > `Live Sessions` to verify current session status
Use `Reports` > `RADIUS` > `Authentication Summary` for historical failed authentications
Use `Reports` > `Endpoints and Users` > `Endpoints` to locate the MAC address
Use `Context Visibility` > `Endpoints` and search by MAC address
Check `Administration` > `System` > `Logging` > `Debug Log Configuration` if deeper troubleshooting is needed
Enable `RADIUS` and `802.1X` debug on the relevant Policy Service Node for detailed failure events
Review `Authentication Failed` events in `Operations` > `System` > `Live Logs` if the failure is not RADIUS-related