Recently I noticed that our online shopping cart (which uses Payflow) is failing for most customers using an American Express card, with error 10576. The response text is "A customer service phone number is required to process transactions. Please add a customer service phone number to your PayPal account or contact PayPal for more info." PayPal's help documentation provides no information about how to resolve this error.
This is exactly what it says: it needs a customer service phone number because American Express has recently become more stringent about requiring it -- they just don't document how to do this, and it's a little unintuitive. It has to be attached to your normal PayPal account, not via the PayPal Manager interface. The steps to follow are below:
This should resolve the error!