Website Payments Pro 4 Paypal

I get the following error when trying the example on DoExpressCheckoutPayment (sandbox):

object(stdClass)#6 (7) { ["Timestamp"]=> string(20) "2008-07-09T00:29:34Z" ["Ack"]=> string(18) "SuccessWithWarning" ["CorrelationID"]=> string(13) "da0d72ceadb15" ["Errors"]=> object(stdClass)#7 (4) { ["ShortMessage"]=> string(95) "Transaction refused because of an invalid argument. See additional error messages for details." ["LongMessage"]=> string(23) "Item amount is missing." ["ErrorCode"]=> string(5) "10430" ["SeverityCode"]=> string(7) "Warning" } ["Version"]=> string(8) "2.400000" ["Build"]=> string(6) "588340" ["DoExpressCheckoutPaymentResponseDetails"]=> object(stdClass)#8 (2) { ["Token"]=> &string(20) "EC-47W04527MN992922D" ["PaymentInfo"]=> string(20) "EC-47W04527MN992922D" } }

and no items get registered on paypal in the purchase. Do you have a clue why is this?


Thank you very much