You cannot create a new customised Tax Event in the User Interface in Business Configuration activity Tax on Goods and Services.
Reproducing the Issue
Go to the Business Configuration Work Centre.
Go to the Implementation Project View and select the relevant one.
Open the Activity list.
Navigate to Fine-tune.
Search for Activity Tax on Goods and Services and open it.
Open Sub-actvity Define Tax Codes.
Click on the Add row button.
Fill in the relevant information for the customised Tax Code: Country, Tax Code (starting with "Z"), Description and Validity.
Now, navigate to the Tax Event column and open the drop down menu:
Only SAP delivered Tax Events are available and there is no possibilities to create a new one.
Since Tax Events are linked to VAT Return submission forms, they are susbjected to very precise legal requirements, hence no customisation or modification is available for these from the User Interface.
If the addition of this new Tax Events is linked to a legal requirement or to a valid business scenario that cannot be fulfilled by using SAP delivered Tax events, this request can be forwarded to our development teams, provided there is legal provision for this addition or impaired Business Processes.
If you need to make such request, please open an incident with Cloud Product Support describing your business scenario in details as well as the new Tax Event needed with all relevant information pertaining to it.
KBA , AP-RC-BCT , Business Config. Tools (SAP Business ByDesign , How To