Whenever you add a credit card to your paypal account, 1$ will be charged to the card by paypal.
It is a process followed by paypal to verify/validate the credit card. By charging this 1$, paypal system identifies whether the card is valid or invalid based on whether the transaction was successful or declined. So if the 1$ charge is successful, the card is a valid card and can be used for future transactions.
This charge is a temporary authorization charge and will be automatically removed / reversed / refunded. So you do not usually have to worry about this charge. But when the charge will be refunded will depend on the card issuer, it is usually reversed in minutes, but may some times extend upto 30 days. If you find the charge not beind reversed for even longer, paypal says you should contact the card issuer(I think you should contact paypal too).
From the information I found online, sometimes there may be multiple 1$ charges, say 2 or 3. The 1 dollar charges normally appear as pending and will be released back.
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