Why does LOV for Tax field on the AR invoice Detail Tax Lines form have no values?

We are on 12.2.12 and setting up AR to use VAT tax.

When we create a new manual invoice in the Transactions form, we select the customer address and the remit to address. On the line, we are entering a description but not choosing an inventory item because our invoices either come from Projects are are manual. When we then click on the Tax button to open the Detail Tax Lines window, we can select the Tax Regime but the Tax field has no values to choose. Going back to the line level, we selected a tax classification but that makes no difference on the Tax window.