If a Domain Name is not renewed within 40 days of expiration, it goes into Redemption, or Pending Delete Restorable status and is deleted from the system. However, your Customers can still redeem the domain name, by clicking on the Restore button and paying the Invoice that is generated. See details
Once the Invoice for Restoration is paid, the system executes the order and sends the Restore command to the Registry. Once this is done, a restore report is generated for the domain name, which is sent to you from email@example.com. You would now have to login to the Registrar Admin Tool, and submit this restore report.
Note that, until you complete the the restoration process and submit the report, the Order would remain Locked in Processing.
The following links explain the process for restoration of domain names with different Registries.