Specify multiple VAT rates for the contract amount

In some cases, a single contract amount includes two different VAT rates (9%/21%).

In this case, the requirement is that amounts can be entered separately from one another.
Example:

€10,000 at 21% VAT
€3,000 at 9% VAT

When creating installment invoices, it is then possible to create an installment invoice based on the amounts themselves and include them in it.