Enter Same "Tax Registration Number" for a Supplier and Customer

We've a German subsidiary which works with a Greek supplier/customer.

The Greek company is already opened in Oracle as a customer. We're now trying to open it as a supplier of our German subsidiary (a separate party).

When we try to update the Tax Registration Number for that supplier, we get an error because the Tax Registration Number is already in use:

This tax registration number is already in use for party type: Third Party and party name: GREEK COMPANY for the same period

We try to override this error by creating a Tax Registration with the German Tax where we enabled the "