Guideline
If you enter an invoice for a customer from another EU country (Transactions > Sales > Create Invoices), the correct tax code is set automatically upon saving the transaction. This applies to items that are marked either as Goods or Services in the Item VAT Type of Nature field in the Item record ( Lists > Accounting > Items).
After you have selected a customer and item, the tax code in the respective column defaults to the one on the Customer record – EC-DUMMY-SE. This is a placeholder while the transaction is being entered.
When you save the transaction, the tax codes defined on the Localization Settings page appear in the Tax Code field.