Thanks for your question!
Unfortunately, you cannot use a service account with the Unity API. Service Accounts are intended for OnBase Services that need to connect to OnBase without a physical user present. Trying to login through the API or any other client with a Service Account will fail.
What you can do as an alternative, is create a new account and give it no product rights, this way it cannot be used to log into any of the OnBase clients, but can still connect through the API.
