Are you trying to export uncorrelated accounts from the API?
If you use the UI, you should be able to click on the Uncorrelated Accounts tab and export the csv file of uncorrelated accounts on a source connection.
It looks like the IDN GUI is using an internal API, /diana, to get the uncorrelated accounts. This API can’t be used by an end user, only by SailPoint.
Instead, this should work for you to at least get the JSON response which can be parsed into the desired CSV format using PowerShell if needed.
GET https://{{tenant}}.api.identitynow.com/v3/accounts?filters=sourceId eq "{{sourceId}}" and uncorrelated eq true