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Go to Administration > Setup > Invoicing elements > Items > create
Fill in the different fields (especially those with red stars) - note that the "billing group" must be Deduction
Click Save and Close once completed
...
...
Go to Administration > Setup > Invoicing elements > Items > create
Fill in the different fields (especially those with red stars) - note that the "billing group" must be Deduction
Click Save and Close once completed
...