Can you prevent discount codes from being applied to Gift Cards? - Govalo Support Center
Can you prevent discount codes from being applied to Gift Cards?
If you are on Shopify Plus, you can add a script to your checkout to make it so discount codes can’t be applied to specific products, such as gift cards.
Alternatively, Shopify allows you to specify whether a discount applies to a specific product or collection, so you may consider having a general collection that includes all products, except gift cards, and set up your discount codes so they can only be applied to that collection.