When trying to update a ticket via the Kayako Classic API, you may the following error:
401 - Unauthorized: Access is denied due to invalid credentials.
You do not have permission to view this directory or page using the credentials that you supplied.
As the error appeared to identify missing permissions, this means you may have attempting to call a STAFF API, which relies on the user permissions associated with the authenticated user.
Please ensure the user you authenticate with has the necessary permissions for the intended changes. If you intend to leverage the REST API instead, be sure each request includes the API key, salt, and signature you generated.
Also, for more information about the API, you can review the Staff API Documentation for more details.