Why Checkout Totals Must Be Recalculated on the Server for Every Order

Online checkouts that accept a total computed in the browser are open to simple tampering, since altering request data can change the price charged. The safer approach is for the server to recompute totals from its own product records on every order. This matters more once a store sells across several currencies and VAT regimes, where extra decisions about tax and currency must also be handled server-side. The author illustrates this with a B2B platform selling waterless urinal systems across 32 European countries. Their checkout calculation function never trusts client-supplied amounts and derives VAT, reverse-charge status and totals directly from product and country data.