2. Common Errors & Fixes

Troubleshoot the most frequent n8n errors.

15m Lesson 2 of 5

Top 10 n8n Errors

401 Unauthorized: Invalid or expired credentials
429 Too Many Requests: API rate limit exceeded
Timeout: Node took too long to respond
JSON Parse Error: Response isn't valid JSON
Expression Error: Invalid expression syntax
No Input Data: Previous node returned empty results
Type Error: Accessing property of undefined
CORS Error: Usually a webhook configuration issue
Memory Error: Processing too much data at once
Connection Refused: Target service is down

Code Examples

Safe Property Access Pattern

javascript

// ❌ Unsafe — crashes if customer is undefined
{{ $json.customer.email }}

// ✅ Safe — returns undefined instead of crashing
{{ $json.customer?.email }}

// ✅ Safe with fallback
{{ $json.customer?.email ?? "no-email@placeholder.com" }}

// ✅ In Code node
const email = item.json?.customer?.email || "fallback@email.com";

Pro Tips

💡Most 401 errors are fixed by re-creating the credential — tokens expire!
💡For 429 errors, add a Wait node or reduce batch size

Comprehension Quiz

Answer 2 of 2 correctly to unlock lesson completion.

1. What typically causes a 401 Unauthorized error?

2. What is the safe way to access a potentially undefined property?

Pass the quiz above to unlock lesson completion

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All lessons in this chapter

1. Reading Execution Logs15m 2. Common Errors & Fixes15m 3. Advanced Error Handling15m 4. Monitoring & Alerting15m 5. Performance Optimization15m