Most sellers are not able to accept credit cards directly. So we use Paypal* as a mediator.
Have you opened a Paypal account?
If the problem is that PP is not accepting your credit card as a backup to your PP account, you should be discussing the problem with them.
EBay no longer owns Paypal.
There are also problems with using debit cards and with using prepaid credit cards.
Are you trying to use one of those to back your Paypal account?
*A few other services are accepted by eBay, but PP is the biggest and best known.
