Why is the amount due mentioned at the centre of the invoice not the same as the balance (EUR) shown in the upper right corner?


The amount due is the amount payable for the enclosed shipment. The balance (EUR) in the upper right corner of the invoice is the total balance of your account. It may differ from the amount due if you had a positive or negative balance on the invoice date. If your account was balanced at the time of invoicing, the two amounts are the same.