The answer is that the service principal lacks the required permissions on the Azure SQL Database. This is the most likely cause of a Power BI JSON policy authentication error because when you configure a data source using a JSON policy with a service principal, Power BI attempts to authenticate via Azure AD, but the service principal must be granted explicit database-level roles—such as db_datareader—to execute queries. Without these permissions, the refresh fails even if the JSON policy syntax is correct, as the underlying authentication handshake cannot access the data. On the PL-300 exam, this scenario tests your understanding of how service principals interact with Azure resources behind JSON-based data source definitions; a common trap is assuming the policy itself is broken when the real issue is missing database permissions. Remember the memory tip: “JSON policy is the key, but the service principal needs the door unlocked—db_datareader opens it.”
PL-300 Prepare the data Practice Question
This PL-300 practice question tests your understanding of prepare the data. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Exhibit
Refer to the exhibit.
// JSON policy for Power BI data source
{
"version": "1.0",
"dataSource": {
"type": "Sql",
"connectionString": "Server=tcp:myserver.database.windows.net,1433;Initial Catalog=mydb;Persist Security Info=False;Encrypt=True;TrustServerCertificate=False"
},
"credentials": {
"authenticationKind": "ServicePrincipal",
"servicePrincipalId": "abc-123",
"tenantId": "tenant-id"
}
}
Refer to the exhibit. You are configuring a data source in Power BI Service using a JSON policy. The data source fails to refresh. What is the most likely issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 does not have permission to the Azure SQL Database.
Option A is correct because when using a JSON policy with a service principal in Power BI, the service principal must have the necessary permissions (e.g., db_datareader role) on the Azure SQL Database. Without these permissions, the data source will fail to refresh, as Power BI cannot authenticate or access the data. The JSON policy itself may be syntactically valid, but the underlying authentication fails due to insufficient database-level permissions.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 service principal does not have permission to the Azure SQL Database.
Why this is correct
Service principal must be granted access to the database.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The version value should be "2.0".
Why it's wrong here
Version 1.0 is valid.
✗
The JSON is missing the 'dataSource' type.
Why it's wrong here
It is present.
✗
The connection string is missing the database name.
Why it's wrong here
It includes Initial Catalog=mydb.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a syntactically correct JSON policy guarantees a successful connection, but Power BI's data source refresh depends on runtime authentication permissions, not just policy structure.
Detailed technical explanation
How to think about this question
Under the hood, Power BI uses Azure Active Directory (AAD) authentication for service principals, which requires the service principal's object ID to be mapped to a database user in Azure SQL Database via the 'CREATE USER [<service-principal-name>] FROM EXTERNAL PROVIDER' command. Without this mapping, the service principal cannot even establish a session, leading to a refresh failure. In real-world scenarios, this is a common misconfiguration when setting up automated refresh with service principals, as the database-level permissions are often overlooked.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Prepare the data — This question tests Prepare the data — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The service principal does not have permission to the Azure SQL Database. — Option A is correct because when using a JSON policy with a service principal in Power BI, the service principal must have the necessary permissions (e.g., db_datareader role) on the Azure SQL Database. Without these permissions, the data source will fail to refresh, as Power BI cannot authenticate or access the data. The JSON policy itself may be syntactically valid, but the underlying authentication fails due to insufficient database-level permissions.
What should I do if I get this PL-300 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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