Gift certificates can only be sold using real-time credit card payment methods. Direct deposit, phone orders, offline credit card processing etc will not sell a certificate code as the customer would be able to then buy products for free as the gift certificate programme creates the code when the order is completed.

In your gift certificates you should note that payment is by immediate credit card payment methods only. If you need to use this method, you should have payment methods active that immediately approve payments as if they are already received by you, otherwise the gift certificate will not be able to be purchased at the checkout.