Use this any time a workflow branches based on conditions (checking message type, checking a value's shape) and there's a real chance the input matches none of the defined rules.
Steps
- Open the Switch (or IF) node doing the branching.
- Look for an Options section, usually a small "Add option" link.
- Find and add Fallback Output.
- Set it to Extra Output (as opposed to "None").
- Save, the node should now show one additional output handle on the canvas.
- Connect that new output to something meaningful, even if it's just a message saying the input wasn't understood, don't leave it dangling.
Gotcha
Without this, any input that doesn't match one of the defined rules simply stops, no error, no log entry, nothing. It looks exactly like a successful run in the Executions tab, which makes this kind of gap especially hard to notice until someone points out that certain messages never got a response.
Quick reference
Checklist for any branching node: does every possible input have somewhere to go, including the case where none of the rules match?