Tax retained by customer?

Tax retained by customer?

Hi,

in Greece, apart from the VAT 21% for which the customer is charged, there is also a 20% tax that is retained by the customer, and he returns to the IRS.

Example:
Net value 100 euros
VAT 21%: 21 euros
Tax 20%: 20 euros

The customer pays 100 + 21, but keeps 20 to return to IRS, so pays 101 euros in total.

How can I put that 20% in the invoice?

Thanks