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Locked and Unlocked Invoices
Salesforce Billing locks invoices from payments when a user makes a charge request to the payment gateway from the Payment Center or a force.com payment site. It also locks invoices after a payment run picks them up for evaluation. The invoice unlocks only when Salesforce Billing confirms that the gateway provides a valid response, or when the payment run finishes processing the invoice. Users must not risk making duplicate payments if the gateway response is indeterminate. (Salesforce Billing Managed Package)

