Module 6 Lesson 5: Debugging API Failures

When an HTTP Request node turns Red, it's usually not n8n's fault. It's the API telling you something is wrong. You must learn the "Language" of HTTP error codes.

1. The 400s (Your Fault)

• 400 Bad Request: You sent JSON that the API doesn't understand (e.g., a missing field).
• 401 Unauthorized: Your API Key is wrong or expired.
• 403 Forbidden: Your Key is correct, but you don't have permission to see this data (e.g., a free key trying to access a pro feature).
• 404 Not Found: The URL is wrong, or the ID you requested doesn't exist.
• 429 Too Many Requests: You hit the Rate Limit (Module 6, Lesson 4).

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2. The 500s (Their Fault)

• 500 Internal Server Error: The other company's server crashed.
• 502 Bad Gateway / 503 Service Unavailable: The API is undergoing maintenance or is overloaded.
• Action: Use Retries (Module 5, Lesson 3) and just wait!

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3. Inspections in n8n

Inside the failed HTTP Request node:

1. Click "Error" -> "Stack Trace."
2. Look at the "Request" tab. Is n8n sending exactly what you thought it was?

• Check: Is the URL https://api.com/null? (This means your variable was empty!).

3. Look at the "Response" tab. Most APIs send a JSON error message like {"error": "Missing field 'email'"}. This is the answer to your problem!

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4. The "Full Response" Setting

In the HTTP Request node settings, you can check "Full Response." This gives you the Headers and Status Code back as data. You can then use an IF node to decide what to do based on the status code (e.g., "If 404, create a new record. If 200, update existing").

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Exercise: The API Hospital

1. Intentionally trigger a 401 Unauthorized error. How does the message differ from a 404 error?
2. Find the "Full Response" setting. Run a successful request. Look at the headers field. What is the content-length?
3. In a production workflow, why should you NOT just "Continue on Error" (Module 5) for a 401 error?
4. Research: What is a "CORS" error, and why does n8n (being a server) almost never have this problem compared to a browser?

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Summary

You have completed Module 6: Connecting to APIs and Webhooks. You can now talk to any API, handle secure authentication, build your own endpoints, and manage the complex realities of large datasets and server failures.

Next Module: Productivity peak: Module 7: Using the Google Workspace Nodes.