10566 american amex buyers check complaining credit customers error express hint integrated letting message pay paypal paypal-pro phane rejected site supported type unsupported

Several of my customers are complaining their Amex card is being rejected with error message "10566 - Credit card type unsupported - The credit card type is not supported. Error". I have integrated e-junkie on my site, with PayPal Pro. Any hint?

Thanks,
Stéphane

This message comes from PayPal. You will want to check with them as to why they are not letting your buyers pay with an American Express card.