Invoice line net amount MUST equal (Invoiced quantity * (Item net price/item price base quantity) + Sum of invoice line charge amount - sum of invoice line allowance amount
PEPPOL-EN16931-R120pxs-taxdata:TaxData/pxs-taxdata:ReportedTransaction/pxs-taxdata:ReportedDocument/pxs-taxdata:DocumentLineu:slack($lineExtensionAmount, ($quantity * ($priceAmount div $baseQuantity)) + $chargesTotal - $allowancesTotal, 0.02)