When Gift Certificate is sold, the sale is recorded in the House Accounts. See Gift Certificates | Sell
When the Gift Certificate is redeemed, it is presented as a payment method by the guest at the time of check out. This means that it is applied to the Guest Folio as any other payment would be applied. In this case, using the Receipt Type "Gift Certificate Redeemed" or whatever you choose to call it. See Gift Certificates | Setup
Since the two transactions (Sold and Redeemed) are recorded in different folios and on different dates, the best way to "match" a Gift Certificate to sold and when it is redeemed is to use the transaction description record details like purchaser name, folio #, gift certificate #, expiry dates, etc.. If you already have a Gift Certificate system set up and have tracking #, then you can use these in the transaction description.
Add Payment Type "Gift Certificate Redeemed" | Payment added to Folio |