Why do some websites want additional card?

[Noele]

Most websites will accept whichever preferred payment method, and I've linked my old BillMeLater Credit as my preferred payment.  BUT A few online sellers want me to add an additional credit card, instead of using PayPal Credit  balance (BML credit) as I have already pre-set?

[sharpiemarker]

Not all merchants accept PayPal Credit and the payment method could simply may not be available for use on a particular purchase as PayPal Credit reserves the right to restrict use depending on the circumstances of each purchase.  If you have not linked a card to your account, depending on what you are buying, the system may request that you add card to as back up or to use instead.  PayPal Credit is an online line of credit, not a "credit card".  Two different things.