Hi there @Ioana ,

Welcome to the Community.

At this time Klaviyo does not have any native feature specific to Shopify Gift Cards, but there are a couple ways to achieve your goal.
 

1. You could create the gift card with the code and sync the code into Klaviyo as a custom property for that profile. From there, you will want to use our property look-up tag to populate the code within the email for that customer. 
   
   You will want to import the gift-card codes through a CSV file and upload them as custom properties: Profile properties reference

 
You can then create a Flow based on a "Placed Order" event where the item = "E-Gift Card."
 
The only concern with this option is that we would not be able to track when the code is used since it's tied to a custom property: This may create more work on your end with having to manually remove the custom property once the code is used. Additionally, you would need to mirror the code in Shopify and set a limit on the usage.
 
2. The second way to achieve this would be by creating a dynamic coupon instead, which will be most feasible in my opinion - More information can be found in the article : How to Create Unique Coupon Codes In Shopify