I'm Miles from the Social Care team at Shopify. Great question! It sounds like you're adding this is as a discount option, but did you know you can offer free shipping in your shipping settings? You can set the conditions (i.e. free shipping over $35) and that way, your customers can receive another discount listed in your discounts. This is a great way to offer free shipping, as you can only apply one discount to an order without the help of an app.
To set up free shipping, follow these steps:
To learn more about offering free shipping in your shipping settings, we have a great guide that walks you through adding it as a default, weight-based or price-based rates. You can even set up free shipping for specific products or customers. Check out the guide here: https://bit.ly/3e1FdId.
As I alluded to earlier, you can only one discount at a time using Shopify's built-in discount tool. If you'd prefer to offer free shipping as a discount, but still allow customers to use other discounts, then you'll need the help of apps from the Shopify App Store. I've recommended some below, but you can find a full list here.
Discount apps come with some other added benefits too.
Unlimited Bundles & Discounts
* Free plan available.
* Setup Product Bundles with different types of discounts that increases the Conversion Rate of your Shopify Store.
* ZERO coding required.
Volume & Tiered Discounts
* Free plan available. 14-day free trial for paid plans.
* Boost order value and sales for your store by incentivizing visitors to add more items to their cart.
* Start making more money right away with quantity breaks & volume discount offers based on how many products a customer buys on your store.
If you do need any further guidance on this, please let me know by replying to this thread.