Unable to Add VAT 0%

-- HikaShop version -- : 3.1.0.
-- Joomla version -- : 3.6.5
-- PHP version -- : 5.6

I add tax VAT 20% and I wanted to add VAT 0% useful when I have to sell overeas.
But it is not possibile because when I add 0% this value overwrite the value 20%.

So, anyone can suggest how to set tax rate to also sell overseas?