In Shopify, you can set free shipping for specific products in the shipping profile settings, but if you purchase a paid product at the same time, shipping fees will be charged. So, if an eligible product is in the cart, you can display a free shipping coupon. Here is an example of how to set it up. (However, since the code can be reused, we recommend limiting its use to one per person.)
Example of setting up to display a coupon for free shipping when purchasing a specific product
[Setup Method 1] Create a free shipping coupon using the normal procedure
[Setup Method 2] Add a customized Liquid section to the cart screen and insert the code
