You should provide an org unit type identified by a valid orgUnitTypeId
(for course offerings, this will be 3
.
For custom org unit types, like "Department", the value will most likely vary LMS to LMS:
You can use the call to retrieve the list of all known org unit types to determine the type corresponding to "Department" for your LMS.
Or, because "Department" is one of the very common custom org unity types, you can use the specific get department-org-unit-type call to find out what the ID is for that type on your LMS (there's also a specific call like this to get the type ID for "semester" org units).