VAT Not Calculating

VAT can automatically be calculated for a PO line by selecting the relevant VAT flag. To do this, click on the Flag icon next to the PO line and click the Microscope icon next to the Tx field. 

The flag can also be added to a line by entering it into the Tx field. A default can be set in User Settings by clicking the Gear icon next to Logout button.  

Usually VAT flags are V for Purchases and S for Sales, with both set to 20%.