In most cases, an amount of €1/£1/$1 showing on your account, in the "pending transactions" section of your Payments tab, is related to one of the merchant security measures to confirm the validity of your payment card.
When you make a payment, a temporary authorization hold for a nominal amount is placed on your card. Merchants use authorization holds to confirm that your payment account is active and has the funds available for purchases.
For example, in the UK, you might see a £1.00 authorization hold. If you live in another country or region, you might see a different amount in the currency of your region.
Authorization holds should expire after a short time (18 days maximum).