Here are some of the PayPal error code which you should correct immediatly
Error:10411-This Express Checkout session has expired. Token value is no longer valid
Reason – It means the user waited long to reach PayPal or make Payment. You need to again show the checkout page.
Error:10409-Express Checkout token was issued for a merchant account other than yours
You are using API credentials of some other account or the API credentials are incorrect.
Error:10434-Value of Custom element has been truncated
You are using custom elements while making express checkout call and the length exceeds permitted value
Error:11607-A successful transaction has already been completed for this token
You are processing the same TOKEN which is already completed. This happen when customer hit back button while making payment. There can be other reason where you might redirecting customer for payment for SAME token again.
Error:10472-CancelURL is invalid
You supplied incorrect value in CancelURL
Some Issue in your name value pair or token is expired
Error:10419-Express Checkout PayerID is missing
Error:10605-Currency is not supported
Error:- PayPal Error