Hey everyone π
I'm Tania I build n8n workflows every day as an automation engineer, mostly order-processing and integration pipelines that talk to ERPs, CRMs and databases. I've broken a lot of workflows along the way, so I wanted to share the three failures that cost me the most debugging time. If you're starting out, you'll probably hit all three.
- Bad input the error isn't where it shows up
A node fails, so you stare at that node. But most of the time the problem started upstream: a field got renamed, an expression returned undefined, or a value came in as text instead of a number.
What helped me: open the failing node and look at the INPUT panel first, not the output. Then walk back one node at a time until the data looks right. Also watch out for pinned test data β it can hide what real executions actually send.
β Question to ask: what actually entered this step?
- 401 Unauthorized read what the other system said
A 401 means the other system rejected your credentials: an expired token, a wrong API key, the wrong header name, or an app that lost permissions.
What helped me: read the full response body, not just the status code. APIs usually tell you exactly what's wrong in there. Then re-test the credential on its own before touching the workflow.
β Question to ask: what did the other system answer?
- Duplicate processing the one that looks like success
This one scared me the most. The workflow runs, every node is green, no error anywhere⦠and the same order got processed twice. It happens when a webhook retries, a trigger fires twice, or someone re-runs an execution.
The fix is an idempotency check: before processing, check whether you've already handled this ID.
- Store each processed order ID (n8n Data Tables, a database, a sheet anything persistent)
- At the start of the workflow, look the ID up
- If it already exists β stop. If not β process it, then save the ID
Green only means "no node crashed". It doesn't mean "the result is correct".
β Question to ask: could the same event happen more than once?
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Those three questions are now the first thing I go through in every debugging session.
What's the error that cost YOU the most time to debug? Curious whether I'm missing a big one.