Most sellers do not directly accept credit cards, even those with "real" businesses that do have merchant accounts.
We did when before we retired and closed our shop, but even then our customers preferred to use Paypal online- even the locals who happily handed over their cards in the shop.
Rather than going to eBay* to learn the problem with adding a US card to a PP account, try asking Paypal.
You should find Help and Contact under Tools at the top of your PP account page.
Or, rather than logging in as just_2474, log in as a Guest.
Guest accounts are allowed to use credit cards directly, although they are actually still going to be processed by Paypal.
As I understand it, the only difference with using a Guest Account and cc directly, is that your coverage is restricted to eBay's Money Back Guarantee and the card's chargeback programme, not the usual 180 day Buyer Protection offered by Paypal.
* EBay was forced to divest itself of Paypal by Wall Street shark Carl Icahn a few years ago. He made a fortune. Nobody else did.