PayPal Transaction Error 10415

PayPal API
PayPal uses an API has a specific set of rules or codes for developing buttons, payments and other coding to integrate PayPal with a website. The Express Checkout PayPal feature, which is associated with error 10415, is based on the PayPal API. The API section of the PayPal Integration Center also lists all of the error codes. In addition to Express Checkout, Website Payments Pro, Recurrent Payments, Mobile Checkout and Mass Payment are all developer applications using the API.
Express Checkout
Transaction error 10415 is an error associated with the PayPal Express Checkout feature. The Express Checkout is a button that gives buyers on the website another option for purchasing. Express Checkout gives the buyer all of the transaction details at the same time, including the order details, shipping options, insurance choice and the total of the taxes. The Express Checkout button has "Check out with PayPal" text written on it. After obtaining the Express Checkout button, the HTML code is then copied and pasted into the website.
Error Code 10415
PayPal Transaction error 10415 means that the transaction was refused because of an invalid argument. While the error may have additional messages, it also indicates that a successful transaction has already been completed for the token. PayPal allows a token only once for a successful transaction. If you determine that your buyers are clicking the "Place Order" button twice, then PayPal recommends that you disable the button after the buyer has clicked it.
Token
Since the transaction error code 10415 means that a successful transaction has been completed for a token, then what is a token? The token is what is returned in the SetExpressCheckout response that executes the "_express-checkout" command. The payment action is taken and then the token is returned. PayPal redirects to the buyer's browser by using the valid token after the buyer has reviewed the PayPal transaction. In the API Express Checkout coding, it is written out as "TOKEN=tokenValue."