First we add the corresponding zero VAT. The line code doesn’t matter.
We set to match variables
We also need to create a new unit of measure as “additive of other values” to add the stamp value to the grand total without affecting the VAT and pre-VAT total.
We open the sales and add to the lines of our document (invoice) the deductions in the order provided. If we want them to be generated automatically, follow the help here.
Reservation, withholding, stamp
The underlying value in this case has been set manually within the item line description. Before the asterisk * (the symbol of multiplication) we write the underlying value that concerns the specific line. Attention for decimal separator we use dot (.).
So in the example in the 1st line (Withholding) the underlying value is 980 euros, in the 2nd (Retention) 980 euros and in the last (Stamp) 0.59 euros.