I know you had your challenges with this one. There is issue 280328, issue 3900790, and KB4477531. The end result in November 2018 was that the code was changed so VAT / Sales Tax was calculated using the invoice amount minus the retention. Before the change it was calculated using the full invoice amount before any subtraction. The real issue is that it is not one OR the other as fixed code. It has to be both as option and the choice should be given when setting up the retention rules. In United Arab Emirates it is the law that VAT must be calculated on the full invoice amount as the retention amount is just a way to give the customer credit. The VAT, or part of the VAT, cannot be postponed until it is time for the customer to pay the retention. You already had both versions in the code. Just not both at the same time, and a choice through setup in place. Obviously the suggestion here is to suggest just that. Kind regards, Henrik Berg Andersen Pingala