Error 401 on setting up RegressionSuiteAutomation Tool

How about this:

1. Regenerate Your PAT with Full Scope
Make sure your token includes:
•    Read & write access to Test Management
•    Project & team access
•    Work items and code access (if needed for test case linkage)
When generating the token in Azure DevOps, select “Full access” or manually check all relevant scopes.
2. Use the Correct Azure DevOps Organization and Project

•    The project name in RSAT matches the one where the test plan lives
•    The organization URL is correct (e.g., https://dev.azure.com/yourorg)
3. Check RSAT Version Compatibility
Some users reported that older RSAT versions don’t handle newer Azure DevOps APIs correctly. Try updating to the latest RSAT version.
4. Verify Test Plan Visibility
Ensure the test plan:
•    Is not private or restricted
•    Is assigned to a team or area path that your PAT user has access to