401 unauthorized response only for a single report when using report pages REST API

[brittaf2002]

Cross posting in case I placed this in the wrong forum. 

We have a customer who is getting a 401 unauthorized only for the report pages API using a service principal. 

They are successfully able to run these APIs without any issue: 

https://learn.microsoft.com/en-us/rest/api/power-bi/groups/get-groups

https://learn.microsoft.com/en-us/rest/api/power-bi/reports/get-reports-in-group

and even https://learn.microsoft.com/en-us/rest/api/power-bi/reports/get-pages-in-group for one report, but this last API doesn't work for one of the other reports, and the error is the following:

HTTP error code 401 Unauthorized. 
 {
  "error" : {
    "code" : "PowerBINotAuthorizedException",
    "pbi.error" : {
      "code" : "PowerBINotAuthorizedException",
      "parameters" : { },
      "details" : [ ],
      "exceptionCulprit" : 1
    }
  }
}

I was not aware of any specific permissions which applies to report pages. Why would we get this error for one particular report? Are there circumstances where we can't query the pages for some reports due to authorization?

[brittaf2002 · Accepted solution]

I'll update this in both places I've posted this question. I found the issue and I believe this is a bug in the REST APIs. The issue occurs when the report uses a dataset belonging to a workspace the service principal doesn't have access to. But why the pages api? The reports in group api works fine. Is there anywhere in the documentation that this is explained?