How do i cancel a PayPal (Express Checkout) transaction?

Question

I have an application that uses Express Checkout to process payments.

I need some way to cancel a transaction after calling SetExpressCheckout (and having the user fill out his details on paypal's page) and before i actually complete it with DoExpressCheckoutPayment.

I can't find the right way to do it in paypal documentation, do i just let it time out or do i need to do some API call?

Answer 1

You just let it time out. If you haven't called DoExpressCheckoutPayment yet, no action has yet taken place.
The token automatically expires after three hours.

Answer 2

Technically you could just empty the token REQUEST, and unset the reshash SESSION and let it expire without risk (assuming you are using the same named variables the api samples came with. What language are you using? I can further provide examples.

In PHP I would simply do:

// empty token
$_REQUEST['token'] = NULL;

//unset reshash session
$_SESSION['reshash'] = NULL;
unset($_SESSION['reshash']);

Now you would ideally want to redirect the user to a cancellation page, something like

header( 'Location: http://www.example.com/transactionCancelled.html' ) 

Otherwise depending if the user is in the 'ReviewOrder' phase, they will just automatically get redirected back to paypal to start a new transaction.