Why did I get API error code 10416?
PayPal returned API error code 10416 - Transaction refused because of an invalid argument.
Cause
You've tried to complete an Express Checkout transaction too many times. An Express Checkout token is valid for 10 transaction attempts, or for three hours, whichever occurs first.
Solution
Restart the Express Checkout process from the beginning with a new SetExpressCheckout request.
Note: See the Developer Portal for a complete list of NVP/SOAP API error codes.