在PayPal REST API中出现500错误

我在PHP应用程序中使用“ paypal / rest-api-sdk-php”，过去一个月在沙盒中进行了完美的测试。今晚移至LIVE以完成产品前的测试，现在得到此响应。

[03-12-2014 01:46:32] PayPal\Core\PPHttpConnection: FINE: Response : {"name":"INTERNAL_SERVICE_ERROR","message":"An internal service error has occurred","information_link":"https://developer.paypal.com/webapps/developer/docs/api/#INTERNAL_SERVICE_ERROR","debug_id":"9a4e0771d4d79"}

我搜索过的任何建议都没有找到合适的答案。

这是我要发送的有效负载（出于安全考虑，已删除了返回的URL）

PayPal\Core\PPHttpConnection: FINE: Payload : 
{"intent":"sale","payer":{"payment_method":"paypal"},"redirect_urls":
{"return_url":"XXX","cancel_url":"XXX"},"transactions":
[{"amount":{"currency":"USD","total":"37.50","details":
{"shipping":"0.00","handling_fee":"2.50","tax":"0.00","subtotal":"35.00"}},"item_list":
{"items":[{"name":"Full Event","description":"This is a full event membership","sku":"547e5ff327a7c","currency":"USD","quantity":1,"price":"35.00"}]},"description":
"Purchase from Site","invoice_number":"547e69aad333b"}]}