No, you cannot create a BOGO for a Gift Certificate Promo.
A Gift Certificate Promo lets you apply an automatic discount based on a percentage or dollar amount off the listed price of an individual Service Certificate or Custom Certificate.
Each Gift Certificate can only be purchased one at a time online.
Multiple Gift Certificates can be included in the same Promotion, but each one is purchased separately. If you create a Promotion that includes multiple Gift Certificates, each one will be listed on its page but will be purchased at a single time. Including multiple Gift Certificates does not mean that the Client is buying all in the same transaction.
You can create a Gift Certificate Promo that's 50% off the listed price of the Service or Custom Certificate. The gift code will still be good for the full value of the Gift Certificate, and if a Client purchases it twice, they'll receive two for the price of one.
Alternatively, you can sell multiple Gift Certificates through the Cash Register. Once you add the first to the Cash Register, add another to bundle the two into one transaction and apply a 50% discount. The Client will pay the discounted rate, but the gift code for each will still be good for the original amount of each Gift Certificate. Gift Certificate Promos are not available for sale through the Cash Register, so select the standard Service or Custom Certificate.