If you see a different amount on your transaction statement than when you made the payment, you may have made a payment in a different currency.
During authentication in the app, when you make a payment of, say, 50USD, 50EUR will currently appear. On your transaction statement, however, this 50USD will be correctly displayed in euros.
It is also possible that an online purchase will not be charged in full until the goods are shipped. At the moment of authorisation, the merchant "reserves" the total amount of your order. If 1 part of your order is shipped, the merchant may choose to "clear" this part already. You will see this appear as 1 transaction in the app. As soon as the other part of your order is sent, this clearing also follows and appears as a separate transaction in the overview.
Finally, if the amount charged in EUR by a merchant differs from the amount in the app, chances are you are dealing with a fraudulent purchase. In that case, pause your card and contact us through our support channels with more info on the transaction in question.