$0.00 の小計で PayPal API を使用しようとすると、次のエラーが表示されます。
[10413] => カート項目の合計金額が注文金額と一致しません。
SetExpressCheckout に渡されるリクエスト データは次のとおりです (個人情報は ... に置き換えられます)。
[0] => L_PAYMENTREQUEST_0_AMT0=9.99
[1] => L_PAYMENTREQUEST_0_NAME0=Name
[2] => L_PAYMENTREQUEST_0_QTY0=1
[3] => L_PAYMENTREQUEST_0_NUMBER0=1
[4] => L_PAYMENTREQUEST_0_AMT1=-9.99
[5] => L_PAYMENTREQUEST_0_NAME1=Discount
[6] => L_PAYMENTREQUEST_0_QTY1=1
[7] => L_PAYMENTREQUEST_0_NUMBER1=0
[8] => PAYMENTREQUEST_0_AMT=2.51
[9] => PAYMENTREQUEST_0_ITEMAMT=0.00
[10] => PAYMENTREQUEST_0_SHIPPINGAMT=2.38
[11] => PAYMENTREQUEST_0_TAXAMT=0.13
[12] => PAYMENTREQUEST_0_SHIPTONAME=...
[13] => PAYMENTREQUEST_0_SHIPTOSTREET=...
[14] => PAYMENTREQUEST_0_SHIPTOSTREET2=...
[15] => PAYMENTREQUEST_0_SHIPTOCITY=...
[16] => PAYMENTREQUEST_0_SHIPTOSTATE=...
[17] => PAYMENTREQUEST_0_SHIPTOCOUNTRYCODE=...
[18] => PAYMENTREQUEST_0_SHIPTOZIP=...
[19] => PAYMENTREQUEST_0_SHIPTOPHONENUM=...
[20] => CANCELURL=...
[21] => RETURNURL=...
[22] => NOSHIPPING=1
[23] => ALLOWNOTE=0
どうすればこれを機能させることができますか?