An invalid argument was passed in your request. This means one of the payment details is incorrect or not supported. For example, a PayPal feature is available only for US Dollars, but the currency is something other than ‘USD’.
For more information on the valid arguments you can use, see the NVP and SOAP API reference.
This error may have other causes based on the API call you're making. See the PayPal Developer Portal for a complete list of all API operations and associated errors.
See the Developer Portal for a complete list of NVP/SOAP API error codes
SetExpressCheckout API call failed (6403 views)