The free shipping progress bar rewards customers with free shipping once they reach a spend threshold. For this to work, you'll need to create a matching free shipping discount in Shopify - the progress bar tracks spend, but Shopify applies the actual discount at checkout.
How to do this?
From your Shopify admin, go to Discounts.
Click Create discount, then select Free shipping.
Under Method, select Automatic discount.
In the Title field, enter a suitable name. This is visible to customers in their cart and at checkout.
Under Countries, select All countries.
Under Customer eligibility, select All customers.
Under Minimum purchase requirements, select Minimum purchase amount and enter the exact spend threshold set in your progress bar.
Under Combinations, if you have product discounts enabled as part of your upsell strategies, select Product discounts here too - this ensures the free shipping discount applies on top of any cart strategy discounts you've configured.
Click Save.
Here's a visual guide to do this.
Note: The minimum purchase amount in step 7 must match your progress bar's threshold amount exactly. A mismatch will cause the bar to show the reward as unlocked without the discount being applied at checkout.