Common Errors and HTTP Status Codes
Status Code Categories
| Range | Meaning |
|---|---|
| 2xx | Success - request was received and processed correctly |
| 3xx | Redirection - further action needed to complete the request |
| 4xx | Client error - something is wrong with the request |
| 5xx | Server error - the server failed to process a valid request |
Frequently Seen Codes
| Code | Common Cause |
|---|---|
| 400 Bad Request | Malformed request body or missing parameters |
| 401 Unauthorized | Missing or invalid authentication credentials |
| 403 Forbidden | Valid credentials but insufficient permissions |
| 404 Not Found | Incorrect URL or resource doesn't exist |
| 429 Too Many Requests | Rate limit exceeded |
| 500 Internal Server Error | Unhandled error on the server side |
Using This as a Debugging Checklist
Matching a failing request's status code against this table is often the fastest way to narrow down whether the problem lies in the request, the credentials, or the server itself.
Course Wrap-Up
From your first request to CI/CD automation with Newman and Docker, you now have a complete, practical foundation for testing and maintaining APIs with Postman.
This brings the Postman API Testing course full circle - from writing your first request to automating and debugging tests at a professional level.
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