[inerg]

Off the top of my head I would say open a Shopify store and find a module that creates a unique order code(Assuming Shopify doesn't do this already). From there build your products for different gift card amounts and then have people redeem the order in store. Most POS f&B systems I assume will let you keep a note for order customization's. In that field I would enter the order code after verifying that the order hasn't been marked delivered in Shopify.

The note keeping isn't super necessary but it can be helpful when trying to track down the order being given to a customer.

In this I'm also assuming Shopify lets you mark orders as pending, delivered, etc. I've only used competitors to it so I'm not 100% sure.