Gift Certificate sometimes has problems

Customer are able to pay for and use GC without problems most of time, however, every once in a while, a customer will pay for the GC, I see a invoice they paid for it, and it shows in paypal, but for some reason, it doesn't issue them an actual GC.

What can I do to resolve this?
Can I make a GC, or only Coupon Codes?

I would like to be able to make GC so when I need to refund customers, they have a GC to use instead of a Coupon Code.

Any help would be greatly appreciated. Thanks.

I see a invoice they paid for it, and it shows in paypal, but for some reason, it doesn't issue them an actual GC

Have those been PayPal e-checks?

Make sure that your Gift Certificates are correctly setup to work with Zen Cart ...

You must have the Product Model set with the first 4 characters as:
GIFT

in uppercase and then you can use anything after ...

and the Product must be marked as:

Product is Virtual: Yes, Skip Shipping Address

On the Modules ... Order Total ... Gift Certificate ot_gv ... and set the queue on:

Queue Purchases
Do you want to queue purchases of the Gift Voucher?

Now when these are ordered, they will be queued for review to ensure that you have recieved valid Payment for them before releasing them ...