It is not possible to add custom item type in the fine tuning activity.
SAP Cloud for Customer.
Reproducing the Issue
Go to the Business Configuration work center.
Go to the Implementation Projects view.
Select the project and click on action Open Activity List.
Search for fine-tune activity name Service Contract and open it.
Click on hyperlink Maintain Item Type .
In the screen which opens, click on add button and try adding custom item type Z1 (where Z1represents the custom item type).
An error Instance with same key Z1 already exists is trigger.
Since there exist custom item type Z1 in another business object fine tune activity under maintain item type.
You need to delete the item type Z1 from other business object fine tune or you need to create another custom item type Z2(where Z2 represents another custom item type) for the Service Contract.
Instance with Same key exist , Maintain Item Type , KBA , fine tuning activity , service contract , LOD-LE-COP-SRV , Service Contract , Problem