Check out our help doc on how to set up a Recharge Checkout Page Widget if you haven't yet
This only works with Recharge and our Post Purchase Offer
After you've set up the widget:
Set the discount type and amount, either fixed (a fixed dollar amount) or percentage, and click 'Save'.
That's it! Go and test it out on your site to see if it works. Notice how the discount applies! Normally this would require the use of Shopify Scripts. Learn more about Shopify Scripts here.