UOM has on hand Inventory. It can not be set as Inactive

Trying to remove a UOM conversion from a temporary class I made., But I get the error:

Not allowed to delete UOM Conversion, only to mark it as Inactive.

So I tried just making it inactive, but get:

UOM has on hand Inventory. It can not be set as Inactive.

I queried the Part master and PartBin tables and find no QOH of any part that uses the UOM, of the Class I’m trying to deactivate.