PL-900 Practice Question: Demonstrate the capabilities of Power Automate
A company has a Power Automate flow that uses a premium connector (e.g., SQL Server). Several users report that the flow fails with a '401 Unauthorized' error. The flow uses a service principal for authentication. What is the most likely cause?
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 service principal's certificate has expired.
Service principal certificates have expiration dates. When the certificate expires, authentication fails with a '401 Unauthorized' error. Option A is incorrect because a wrong connection string would produce a different error (e.g., 'Cannot connect to SQL Server'). Option B is irrelevant as the environment does not affect authentication. Option C is incorrect because rate limits cause '429 Too Many Requests', not 401.
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 SQL Server connection string is incorrect.
Why it's wrong here
A malformed connection string typically yields a connection or login failure, not a 401, which signals rejected credentials or an unconsented service principal. It is tempting because connection strings are the usual suspect for SQL Server connectivity faults, and would be correct if the error were a timeout or 'server not found'.
- ✗
The flow is not in the default environment.
Why it's wrong here
Environment placement does not govern authentication; a flow in a non-default environment still authenticates normally, so it cannot produce a 401. It is tempting because premium connectors and environment policies are commonly confused, and environment choice would matter if the connector were blocked by a data loss prevention policy.
- ✗
The flow is exceeding API rate limits.
Why it's wrong here
Rate limiting returns HTTP 429 with a Retry-After header, not 401, which specifically denotes failed authentication or an unconsented service principal. It is tempting because throttling is a frequent cause of intermittent flow failures, and would be correct if the flow failed only under high-volume bursts.
- ✓
The service principal's certificate has expired.
Why this is correct
An expired certificate breaks the service principal's client credential, so Microsoft Entra ID rejects the token request and the connector returns 401 Unauthorized. This directly satisfies the stem's authentication-failure constraint: the flow authenticates as a service principal, whose certificate-based secret must remain valid for token issuance to succeed.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PL-900 practice question is part of Courseiva's free Microsoft certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PL-900 exam.