202123 - FortiOS Version Does Not Support the Monitor Endpoint

Agent error code #202123 indicates that the FortiOS running on the target device does not provide the monitor endpoint the agent needs. The device answered, and the API surface Knocknoc relies on is not present in that version.

Common causes include:

• The FortiGate runs a FortiOS version older than the one that introduced the endpoint
• The device is a model that exposes a reduced API surface
• A firmware downgrade removed an endpoint that was previously available

Steps to Resolve

Check the FortiOS Version

1. On the FortiGate, go to System > Settings and note the firmware version, or run get system status from the CLI
2. Compare it against the minimum version documented on the Fortinet setup guide

Upgrade the Firmware

Upgrading the FortiGate to a supported FortiOS release is the direct fix. Follow Fortinet's upgrade path guidance rather than jumping versions.

Use a Different Knoc Mode

If the device cannot be upgraded, a different Fortinet mode may suit it. The address group and external feed approaches use different endpoints and have different version requirements. See the Fortinet setup guide for what each mode needs.

Run the Knoc Validator

Open the knoc and run Validate. The agent reports which capability check failed against this device.