This is how I handle gift certificates in my shop. You can click on this listing for more info:
https://www.etsy.com/listing/104803491/gift-certificate-50-dollars-good-on-anyHOW THE GIFT CERTIFICATES ARE REDEEMED AT THE MERRY MAENAD:
(instructions will be sent along with the certificate)
• Each Gift Certificate comes with a unique validation code.
• When the Recipient makes a purchase, s/he would click on “Other” as the payment method and enter the validation code into the Note to Seller section
• I would then send a separate invoice from Paypal with any remaining balance after the certificate is applied to the total due. The remaining balance could then be paid from the Recipient’s Paypal account or by credit card via Paypal.
• If the certificate is worth more than the total, the remaining balance would be issued as store credit for future use (redeemable with the same validation code and in the same manner as the Gift Certificate)