Question 524 of 989
200-901 Infrastructure and Automation Practice Question
A developer is using Python requests library to interact with a Cisco IOS XE device's REST API. The call returns a 400 Bad Request status. The payload is correctly formatted JSON. What is the most likely cause?
⚠ Common exam trap
Cisco often tests the distinction between 400 Bad Request (client-side syntax/header issues) and 401 Unauthorized (invalid credentials), tricking candidates into assuming authentication errors always return 401, when in fact missing or malformed authentication headers can trigger a 400.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The authentication credentials are missing or incorrect in the request header
A 400 Bad Request status from a Cisco IOS XE REST API indicates a client-side error, typically related to malformed syntax or missing required elements. Since the JSON payload is confirmed as correctly formatted, the most likely cause is missing or incorrect authentication credentials in the request header, as the API requires valid credentials (e.g., Basic Auth with username:password encoded in Base64) to process the request. Without proper authentication, the server rejects the request with a 400 status before even evaluating the payload.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The authentication credentials are missing or incorrect in the request header
Why this is correct
400 Bad Request commonly indicates missing or invalid authentication headers.
- ✗
The device's API service is not enabled
Why it's wrong here
If the service is disabled, the request would likely timeout or return a connection refusal.
- ✗
The requested URL path is incorrect
Why it's wrong here
An incorrect URL would typically result in a 404 Not Found, not 400.
- ✗
The JSON payload contains a syntax error
Why it's wrong here
The stem says payload is correctly formatted.
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Last reviewed: Jun 24, 2026
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