I generate release note automatically when ever the build is triggered. My aim is to create a wiki page from the release note. I followed the powershell script on https://scatteredcode.net/publishing-release-notes-to-tfs-vsts-wiki-during-release/
The script ran successfully but the wiki sub page did not get created. The aim is to create a sub page "test" under the PartsUnlimitedWiki page.
PowerShell Script

I tested with below PowerShell script, and it can work will to create/update the sub-page with the content. You can reference it to update your script.
When you run the script in Azure Pipelines, the value of authorization token can be either your PAT (Personal Access Token) or the
System.AccessToken(Job access token). You can follow the documentation "Job access tokens" to check and assignSystem.AccessTokenwith the required permissions to access Wiki.