Upsell Support: How do I set a free shipping minimum?

Go to the Shopify Admin > Settings > Shipping and delivery and open the relevant Shipping profile.

Add a Shipping zone to this profile.

Add a Shipping Rate to this zone.

Add a Condition and select Based on order price. Enter a minimum order price that is the same value as the free shipping threshold in the app. In this example, $25 orders get free shipping.
When you're finished, click Done.

More details here from Shopify on setting up free shipping rates.