Uniconta doesn't enter the VAT codes until the offset account is entered in the journal.
If the offset account is not entered on the same journal line then Uniconta will retrieve the VAT account from the line on which the offset posting is entered.
Users can also uset the "Set up Journal" button in the General Journals menu and select to "Use Customer/Vendor VAT in journal".
If this field is selected then users must remember to enter the ledger account first and then the vendor/customer account as an offset account. Otherwise the VAT code cannot be retrieved from the customer/vendor.