I'm looking for an event that is always fired just before Magento captures the payment. The reason is that the Magento is integrated into an external system (events registration) and therefore needs to check the availability just before charging the credit card - if no spots are available I'd need to throw an error and redirect the user.
Is there a reliable event that I can get my observer to listen on? Or should I hard code a custom event into the payment system? (There's only 1 payment method).