错误是我有一个returnURL和CancelURL，其值为'0'，因为我试图将其连接为带有+(JavaScript习惯)的字符串，但是由于Laravel的路由，baseUrl()返回的地址无效.

The Error was I had a returnURL and CancelURL with a value of '0' because I was trying to concatenate to strings with a + (Javascript habit) but also the baseUrl() returns an invalid address due to Laravel's routing.

查看PayPal.log很有帮助

It was helpful to look at the PayPal.log