Question about withholding tax on invoicing

I am an architect (self-employed) and work with invoices on which withholding tax is deducted by the client. However, since I started invoicing with Dexxter, I cannot find where to correctly enter this deduction on my invoices (as a separate deduction/retention, not as a discount or performance rule).

Is there an option in Dexxter to add withholding tax as a deduction, and if yes, where can I activate this function?

If this is not provided as standard: what is the correct accounting method for processing this on the invoice, according to Dexxter?

Thank you in advance for your help.