Autotask PSA SSO configuration can be found at the following url: https://ww13.autotask.net/help/Content/AdminSetup/1FeaturesSettings/ResourcesUsers/Security/SSSO_OIDC.htm
For the configuration part of Workspace ONE Access SSO you can see the available API at this url: https://code.vmware.com/apis/57/idm#/
The problem is that Autotask PSA SSO doesn’t work/supports the setup of VMware Workspace ONE Access. I worked around this issue by having a federated setup to our Office 365 tenant and adding the Autotask application there and ultimately publishing the application as a custom application link and still provide the requested SSO.
Add a Web Application Link in Workspace ONE Access and provide the following as your target url: