How to use advanced settings for WooCommerce
If you need to specify more advanced settings for generating your discount codes, you can use the Advanced settings dialogue. This allows you to specify all properties available in WooCommerce Coupon API. This is an advanced setting and requires that you perform tests to make sure that the codes are generated correctly.
Only allow the discount to work on specific product categories
The "product_categories" property allows you to specify one or more categories that the discounts will be entitled to. To set this property, you enter the category ID(s): "product_categories":  or if you have multiple: "product_categories": [12345, 6789]
If you need to find the ID for a specific category, WooCommerce has an article that shows you how you can find it: Find Product Category IDs
Here's how it would look in the advanced settings: