Field help (SALPRITYPC) 

These two radio buttons, initialized from the BP, are used to define whether the amounts on the invoice lines are entered as Tax excl. or Tax inc.

The choice between Ex-tax or Tax-incl. is only possible upon invoice creation.

If the DEPMGTMOD - Discount management mode parameter (TC chapter, INV group) has the value Rebate on VAT, the type of amount is Ex-tax by default, regardless of the value of parameter SALPRITYP - Amount/Price type (TC chapter, INV group). You cannot select Tax-incl..